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diff --git a/38308-8.txt b/38308-8.txt new file mode 100644 index 0000000..e79c9f5 --- /dev/null +++ b/38308-8.txt @@ -0,0 +1,4055 @@ +The Project Gutenberg EBook of Natural History of Cottonmouth Moccasin, +Agkistrodon piscovorus (Reptilia), by Ray D. Burkett + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Natural History of Cottonmouth Moccasin, Agkistrodon piscovorus (Reptilia) + +Author: Ray D. Burkett + +Release Date: December 15, 2011 [EBook #38308] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK NATURAL HISTORY OF *** + + + + +Produced by Chris Curnow, Joseph Cooper and the Online +Distributed Proofreading Team at http://www.pgdp.net + + + + + + + +Transcriber's Note. + +[=X] in Table 12 represents "x bar" or "x overbar" (the mean value). + +Hyphenation has been standardised save for the contents of 'Literature +Cited' and the 'List of Publications.' + + + + + ================================= + + UNIVERSITY OF KANSAS PUBLICATIONS + MUSEUM OF NATURAL HISTORY + + Vol. 17, No. 9, pp. 435-491, 7 figures in text + ------------ October 27, 1966 ---------------- + + Natural History of Cottonmouth Moccasin, + Agkistrodon piscivorus (Reptilia) + + BY + + RAY D. BURKETT + + UNIVERSITY OF KANSAS + LAWRENCE + 1966 + + + + + UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY + + + Editors: E. Raymond Hall, Chairman, Henry S. Fitch, + Frank B. Cross + + Volume 17, No. 9, pp. 435-491, 7 figures in text + Published October 27, 1966 + + UNIVERSITY OF KANSAS + Lawrence, Kansas + + PRINTED BY + ROBERT R. (BOB) SANDERS, STATE PRINTER + TOPEKA, KANSAS + 1966 + +[Illustration: Printer's Logo] + + 31-4629 + + + + + Natural History of Cottonmouth Moccasin, + Agkistrodon piscivorus (Reptilia) + + BY RAY D. BURKETT + + + + +CONTENTS + + + PAGE + INTRODUCTION 439 + ACKNOWLEDGMENTS 440 + SYSTEMATIC RELATIONSHIPS AND DISTRIBUTION 441 + DESCRIPTION 444 + Color and Pattern 444 + Scutellation 444 + Dentition 449 + HABITAT AND LIMITING FACTORS 450 + REPRODUCTION 452 + Courtship and Mating 452 + Reproductive Cycles 452 + Embryonic Development 454 + Birth of Young 454 + Number of Young per Litter 454 + Population Composition 455 + Reproductive Potential 455 + GROWTH AND DEVELOPMENT 456 + Size at Birth and Early Growth 456 + The Umbilical Scar 457 + Later Growth and Bodily Proportions 457 + SHEDDING 459 + The Shedding Operation 459 + Frequency of Shedding 460 + FOOD HABITS 461 + Methods of Obtaining Prey 461 + Food and Food Preferences 462 + MORTALITY FACTORS 465 + Natural Enemies and Predators 465 + Parasites and Diseases 465 + Miscellaneous Causes of Death 466 + BEHAVIOR 466 + Annual and Diel Cycles of Activity 466 + Basking 469 + Coiling 469 + Locomotion 470 + Disposition 470 + Defense and Escape 471 + "Head Bobbing" 471 + Combat Dance 472 + THE VENOM 473 + Properties of the Venom 473 + Venom Yield and Toxicity 473 + Susceptibility of Snakes 475 + THE BITE 476 + Effects of the Bite 476 + Treatment 477 + Case History of a Bite 479 + Snakebite in the United States 480 + SUMMARY 480 + LITERATURE CITED 485 + + + + +INTRODUCTION + + +Objectives of the study here reported on were to: (1) learn as much as +possible concerning the natural history and economic importance of the +cottonmouth; (2) determine what factors limit its geographic +distribution; (3) determine the role of the cottonmouth in its +ecological community; and (4) compare the cottonmouth's life history +with that of other crotalid snakes, especially the kinds that are most +closely related to it. + +Twenty-five live cottonmouths were kept in the laboratory for the +purpose of studying behavior and fang shedding and for comparison of +measurements with those of preserved specimens. Live snakes were +obtained in Brazoria and Nacogdoches counties, Texas, from Hermann Park +Zoo, Houston, Texas, and from the late Paul Anderson of Independence, +Missouri. Preserved western cottonmouths were examined for the purpose +of determining variation, distribution, food habits, body proportions, +embryonic development, and reproductive cycles. The cottonmouths +examined include: 221 from Texas; 33 from Arkansas; 22 from Louisiana; 2 +from Illinois; and 1 each from Kansas, Mississippi, and Oklahoma. + +In the preparation of this report I have examined all available +literature pertaining to the cottonmouth and have drawn from these +sources for comparative or additional material. Some of the more +noteworthy contributions to knowledge of the cottonmouth are the general +accounts of the life history by Allen and Swindell (1948), Barbour +(1956), and Wright and Wright (1957); the publications by Gloyd and +Conant (1943) concerning taxonomy; Klimstra (1959) concerning food +habits; and Allen (1937), Parrish and Pollard (1959), Swanson (1946), +and Wolff and Githens (1939b) concerning the venom. Numerous other +publications, although brief, contain worthwhile contributions. Also of +special interest as a source of material for comparison of cottonmouths +with other crotalids are the works of Fitch (1960) on the copperhead and +of Klauber (1956) on the rattlesnakes. + +The cottonmouth has been well known for nearly 200 years. Wright and +Wright (1957) listed the following vernacular names that are applied to +the cottonmouth: black moccasin, black snake, blunt-tail moccasin, +congo, copperhead, cottonmouth water moccasin, cotton-mouthed snake, +gapper, highland moccasin, lowland moccasin, mangrove rattler, moccasin, +North American cottonmouth snake, North American water moccasin, North +American water viper, pilot, rusty moccasin, salt-water rattler, +stubtail, stump (-tail) moccasin, stump-tail viper, swamp lion, Texas +Moccasin, trapjaw, Troost's moccasin, true horn snake, true water +moccasin, viper, water mokeson, water pilot, water rattlesnake, and +water viper. + +Some of the names listed above are based upon superstition and folklore +prevailing in pioneer times, and others are based upon the behavior or +appearance of the snake at various ages. Names like "stump-tail +moccasin" are derived from the appearance of females which have short +tails or snakes that have lost part of the tail. Names like "gapper" and +"trapjaw" came to be applied because of the habit of the snake's lying +with its mouth open when approached. The name "cottonmouth" also was +derived from this behavior, although the lining of the mouth is whitish +in most other snakes. The term "rattlesnake" may have come from the fact +that the cottonmouth vibrates its tail vigorously when nervous as do +many other snakes, or it may have been confused with rattlesnakes. +Because of the general public's fear of snakes and their reluctance to +learn to discriminate between the poisonous and harmless species, +numerous kinds of snakes seen in or near water have been called +moccasins. The general appearance, pugnacious behavior, and whitish +mouth of water-snakes (_Natrix_) have earned them a bad reputation. In +fact, a great majority of the "cottonmouths" reported in many areas are +found to be water-snakes. + +The cottonmouth is economically important mainly because of the +injurious or fatal effects of its bite and the psychological effect that +its actual or suspected presence has upon many persons. The species eats +a wide variety of prey items and helps to prevent overabundance of +certain kinds of organisms. The venom has been used in the therapeutic +treatment of blood clots owing to its anticoagulant properties +(Didisheim and Lewis, 1956). It also is employed in the treatment of +haemorrhagic conditions and rheumatoid arthritis, as well as in the +production of antivenin (Allen and Swindell, _op cit._:13). None of +these uses of venom has become widely accepted, and its value is +questionable. + + + + +ACKNOWLEDGMENTS + + +For guidance in the course of my study, I am especially indebted to +Professor Henry S. Fitch. For suggestions concerning the preparation of +the manuscript, I thank Professor E. Raymond Hall. I am grateful to my +wife, Janis, for her invaluable assistance and for typing the +manuscript. + +For use of specimens in their care, I thank Professors William E. +Duellman, University of Kansas; Robert L. Packard, formerly of Stephen +F. Austin State College; W. Frank Blair, University of Texas; and +William B. Davis and Richard J. Baldauf, Texas Agricultural and +Mechanical College. Mr. John E. Werler of the Hermann Park Zoo, Houston, +Texas, contributed live individuals; Mr. Richard S. Funk contributed +information on the birth of a brood of cottonmouths; and Dr. Henry M. +Parrish contributed information on the incidence of snakebite. To +numerous other persons at leading museums throughout the United States +for information on the cottonmouths in their collections, to all who +helped with the field work in various ways, and to others at the +University of Kansas for their help and suggestions I am grateful. + + + + +SYSTEMATIC RELATIONSHIPS AND DISTRIBUTION + + +Snakes of the genus _Agkistrodon_ are relatively primitive members of +the Crotalidae, which is one of the most specialized families of snakes. +A majority of the pit-vipers are found in the Americas, but close +relatives are found from extreme southeastern Europe through temperate +Asia to Japan (_A. halys_) and southeastern Asia including Indonesia +(_Agkistrodon_ and _Trimeresurus_). Familial characters include: +vertical pupil of the eye; facial pit present between the preoculars and +loreal; scales usually keeled; short, rotatable maxilla bearing a large +hollow fang; toothless premaxilla; chiefly hematoxic venom; and +undivided anal plate. + +The genus _Agkistrodon_ includes about nine species in the Old World and +three in North and Central America. Some of the primitive characters of +the genus are: head covered with nine enlarged shields or having the +internasals and prefrontals broken up into small scales; subcaudals on +proximal part of tail undivided; fangs relatively short; tail lacking +rattles. In one species, _A. rhodostoma_, the scales are smooth; and the +female is oviparous and guards her eggs until they hatch. Other species +have keeled scales and are ovo-viviparous. + +There is little paleontological evidence illustrating evolution of the +cottonmouth or for that matter of crotalids in general. Brattstrom +(1954) summarized the current knowledge of fossil pit-vipers in North +America. The few fossils found of the cottonmouth are from Alacha, +Brevard, Citrus, Levy, Pasco, and Pinellas counties, Florida +(Brattstrom, _op. cit._:35; Auffenberg, 1963:202). All are of late +Pleistocene Age and well within the present geographic range of the +cottonmouth. + +Of crotalid genera only _Agkistrodon_ occurs in both the Old World and +the New World, suggesting that this genus is relatively old. Schmidt +(1946: 149-150) mentioned several other closely related groups of +animals found in both eastern Asia and eastern North America, including +the reptilian genera: _Natrix_, _Opheodrys_, _Elaphe_, _Ophisaurus_, +_Leiolopisma_ (= _Lygosoma_), _Eumeces_, _Clemmys_, _Emmys_, and +_Alligator_. Of the groups of animals now confined to these two regions +the most important are the cryptobranchid salamanders, the genus +_Alligator_, and the spoon-bills (_Psephurus_ in China and _Polyodon_ in +the Mississippi drainage). Fossil evidence for these groups indicates +that existing forms common to eastern Asia and eastern North America are +remnants of a late Cretaceous or early Tertiary Holarctic fauna which +was forced southward as the climate became gradually cooler to the +north. "Other clues suggest that both _Agkistrodon_ and _Trimeresurus_ +(_Bothrops_) moved from Asia to America, one of these presumably giving +rise to the rattlesnakes." (Darlington, 1957:228). + +The named, American kinds of _Agkistrodon_ currently are arranged as +three species: the copperhead, the cantil and the cottonmouth. The +copperhead (_A. contortrix_) is divided into four subspecies, all of +which are terrestrial. This species occurs from southern New England to +eastern Kansas and along the Atlantic and Gulf Coastal plains, exclusive +of peninsular Florida and the delta of the Mississippi River in +Louisiana. It extends southwest from Kansas through the Edwards Plateau +of west-central Texas. Isolated populations occur in the Chisos and +Davis mountains of Trans-Pecos Texas. The cantil or Mexican moccasin +(_A. bilineatus_), probably the nearest relative of the cottonmouth (_A. +piscivorus_), is divisible into two subspecies and occupies a nearly +complementary range from Mexico south to Nicaragua. The cottonmouth +occurs throughout the coastal plains of the southeastern United States, +usually at altitudes of 500 feet or less. Two subspecies are recognized, +the eastern _A. p. piscivorus_ and the western _A. p. leucostoma_. A +revision of the genus is underway by Professor Howard K. Gloyd. + +The basic pattern and various behavioral traits are common to all three +species. The young are more nearly alike in appearance than adults, the +copperhead and the cottonmouth being easily confused. Adults differ in +color, size, body proportions, habitat, and habits. In range and habitat +preference the cottonmouth more closely resembles the southern +subspecies of the copperhead, _A. c. contortrix_, which is usually found +in lowlands, near swamps and streams, but seldom in water. + +[Illustration: FIG. 1.] + +FIG. 1. Geographic range of the cottonmouth, showing marginal and +near-marginal records, based largely upon maps by Gloyd and Conant +(1943:165) and Conant (1958:336) but including additional records. The +more important of these records (from east to west) are discussed in the +following paragraphs. Crosshatching indicates the area of intergradation +between the eastern and western subspecies. Old records, indicated by +dates, and their sources are as follows: 1850's and 1891--U. S. National +Museum numbers 4263 and 32753 respectively; 1897--Hurter (1897); and +1895--Stejneger (1895:408). + +The northernmost record for the eastern subspecies is in the Petersburg +area, Prince George County, Virginia (Anon., 1953:24). A sight record +(Hickman, 1922:39) near Bristol, West Virginia, probably was based on a +water-snake (_Natrix_ sp.), since the stream in which the snake was seen +flows north into the Ohio River rather than southeast through Virginia. +In North Carolina the most inland record is from the Neuse River, six to +eight miles east of Raleigh (Stejneger, 1895:408). Neill (1947:205) +reported a population in the vicinity of Dry Fork Creek on the boundary +line of Wilkes and Oglethorpe counties, Georgia. Distribution of +cottonmouths in Florida is statewide, including the Keys and other +offshore islands. + +The ranges of the two subspecies, _piscivorus_ and _leucostoma_, meet +near the eastern border of Mississippi. _A. p. piscivorus_ has been +reported from Tishomingo County to the Gulf and east of the Loess Bluff +area in central Mississippi, and _A. p. leucostoma_ has been reported +from this area westward. A few specimens from along the Coast indicate +intergradation (Cook, 1962:33) between the two subspecies. + +Barbour (1956:33) reported one specimen from Cypress Creek, in the Green +River drainage, Muhlenberg County, Kentucky, and stated that suitable +habitat can be found in several areas east of Kentucky Lake. Hence, +cottonmouths may have entered this area via the Ohio River. Stejneger +(_loc. cit._) reported the species in the Wabash River at Mount Carmel, +Wabash County, Illinois, and mentioned a former occurrence at Vincennes, +Knox County, Indiana; but there are no recent records at these +localities. Hurter (1897) reported having seen cottonmouths in Illinois, +opposite St. Louis; Smith (1961:265) believes that this and a population +in Monroe County, Illinois, are isolated relicts, since no specimens +have been found within 50 miles to the south of Monroe County. The +specimens reported by Anderson (1941:178; 1945:274) near Chillicothe +(three miles southwest and seven miles northwest, respectively), +Livingston County, Missouri, also are thought to represent a relict +population. Hall and Smith (1947:453) reported one specimen from Jasper +County, Missouri, in the Spring River which flows through extreme +southeastern Kansas and into Oklahoma and another in the Neosho River at +Chetopa, Kansas. Both of these specimens were taken after a flood, and +no additional specimens have been taken in this region. Nevertheless, +sufficient habitat is probably available along the Neosho and Verdigris +rivers in the southeastern part of Kansas. + +In Texas the cottonmouth has penetrated marginal habitat perhaps farther +than anywhere else in its range. Formerly it was thought to be limited +to the country east of the Balcones Escarpment (Smith and Buechner, +1947:8), but semiarid areas of the state have been invaded primarily via +the Colorado and Brazos River systems up to altitudes of 2300 feet. Two +additional specimens are said to have been collected along the Rio +Grande. Dr. Howard K. Gloyd (_in litt._) stated that the specimen +reported from Eagle Pass, Maverick County, is believed to have been +taken in the 1850's; and the one said to have come from the mouth of the +Devil's River is actually marked "near Santa Rosa, Cameron County, +September 30, 1891." No additional specimens have been taken in that +area; and the range now probably extends no farther south than Corpus +Christi, Texas. Brown's (1903:554) knowledge of the extension of the +range of the cottonmouth west of longitude 98° is probably based upon +the records along the Rio Grande reported in the nineteenth century. + +Three extensions of the known range in Texas are reported herein. One +specimen was captured by Mr. Harry Green (HWG 346) along the San Saba +River, 8.1 miles west of Menard, Menard County. The other two specimens +(KU 84375 and 84376) were taken by the late Paul Anderson one and +one-half miles north of Pecan Crossing, South Concho River, Tom Green +County, and one mile west of Mertzon, Irion County. + +In the hypsithermal period following Pleistocene glaciation, +cottonmouths gradually moved northward occupying areas beyond their +present range. The distributional records since the 1850's and the +apparent relict populations now in existence indicate that the range +of this species has since receded. + + + + +DESCRIPTION + +Color and Pattern + + +Color predominantly brown, ranging through pale reddish-brown or dark +reddish-brown, brownish-green, to almost black; 10 to 17 irregular dark +brown bands on paler brown ground color; young paler (some nearly salmon +pink), retaining a vivid pattern throughout first year; pattern of most +individuals nearly obliterated by third year; brilliance and dullness of +predominant color correlated with molting cycle (skin especially bright +and shiny immediately following shedding); tip of tail yellowish in +juveniles; posterior part of venter and tail uniformly black in some +adult individuals, especially females; secondary sexual differences in +dorsal coloration, such as found in copperhead by Fitch (1960:102), not +noted. + +The eastern subspecies, _A. p. piscivorus_, has the more brilliant +pattern in which the centers of the dark cross-bands are invaded by the +ground color. The cross-bands are slightly constricted in the mid-line +and may or may not be bilaterally symmetrical. One-half of the +cross-band may be displaced anteriorly or posteriorly to a slight degree +or may even be completely absent. From one to several dark spots may be +present within the cross-bands. + +The western subspecies, _A. p. leucostoma_, has a comparatively dull +pattern in which the ground color does not invade the center of the +cross-bands. In many instances the bands are outlined by white scales, +as in the Mexican moccasin (this character is not so prominent in _A. p. +piscivorus_ because of the paler ground color). A large, dark blotch +usually occurs at the base of the cross-band and may completely cross +the ventral scales. The characteristic variations found in _piscivorus_ +are also present in _leucostoma_. + +The number of bands is often difficult to count because of the dark +color of some specimens. Gloyd and Conant (1943:168) reported averages +of 12.5 (11 to 16) and 12.2 (10 to 16) in males and females, +respectively, of _leucostoma_ and ranges of 10 to 17 for males and 10 to +16 for females with averages of 13 in both sexes of _piscivorus_. On 20 +specimens of _leucostoma_ from Texas the average number of bands was +12.7 (11 to 15). If the number of bands differed on the two sides of an +animal, the total number of the two sides was divided by two. + + +Scutellation + +The scutellation of the cottonmouth closely resembles that of the other +species of _Agkistrodon_. For example, the nine cephalic shields are +characteristic of most species of _Agkistrodon_, as well as most other +primitive crotalids and viperids, and most colubrids. Most individuals +have an additional pair of large scales behind the parietals. + +The numbers of postoculars, supralabials, and infralabials are variable. +On either side the postoculars (three in most specimens) are reduced to +two in some specimens. The supralabials (eight in most specimens) +frequently vary (usually on one side only) from seven to nine. The +number of infralabials is somewhat more variable than the number of +supralabials, the usual number being 11, but 10 is also common; 8, 9, +and 12 are more rare (Table 1). In 102 snakes in which these characters +were examined, four different combinations of supralabials and seven +combinations of infralabials were found. Both characters together +yielded 16 combinations, considering only the actual number of scales +and not taking into account the side of the head on which they occurred +(Table 2). The combinations found in a brood of seven young from +Houston, Texas, are shown in Table 3 to illustrate the variability of +this character. Gloyd and Conant (1943:168) found a variation of 6 to 11 +(8) and 7 to 9 (8) supralabials and 8 to 13 (11) and 8 to 12 (10.4) +infralabials in samples of 301 _leucostoma_ and 119 _piscivorus_, +respectively (numbers in parentheses represent average). Also of +interest is the variability of the scales themselves. In one instance a +scale was found that had not completely divided. In another specimen the +last supralabial and last infralabial were one scale that completely +lined the angle of the jaw. Instances of one scale almost crowding out +another were common. In still other instances one or two supralabials +were divided horizontally into two scales. Individual variation rather +than geographical variation occurs in these characters. + + TABLE 1.--Frequency of Occurrence of Various Numbers of + Supralabial and Infralabial Scales in 102 Cottonmouths. + + ==================================================== + | |Specimens |Specimens | | | + |Number |having |having |Total |Percentage | + |of scales |number on |number on | | | + | |both sides |one side | | | + |----------------------------------------------------| + | Supralabials | + |----------------------------------------------------| + | 7 | 11 | 24 | 35 | 25.2 | + | 8 | 64 | 27 | 91 | 65.5 | + | 9 | 0 | 3 | 3 | 2.2 | + |----------------------------------------------------| + | Infralabials | + |----------------------------------------------------| + | 8 | 0 | 2 | 2 | 1.5 | + | 9 | 3 | 10 | 13 | 9.6 | + | 10 | 12 | 32 | 44 | 32.4 | + | 11 | 53 | 22 | 75 | 55.1 | + | 12 | 0 | 2 | 2 | 1.5 | + ---------------------------------------------------- + + TABLE 2.--Numbers of Supralabials and Infralabials of 102 + Cottonmouths. + + =========================================== + | Number of | Number of | Number of | + | individuals | supralabials | infralabials | + | 37 | 8 | 11 | + | 15 | 8 | 10-11 | + | 12 | 7-8 | 11 | + | 6 | 7-8 | 10-11 | + | 5 | 8 | 10 | + | 5 | 8 | 9-10 | + | 4 | 7 | 11 | + | 3 | 7 | 9-10 | + | 3 | 7-8 | 10 | + | 2 | 7 | 9 | + | 2 | 7 | 10 | + | 2 | 8 | 10-12 | + | 2 | 8-9 | 10 | + | 2 | 7-8 | 8-9 | + | 1 | 7-8 | 9 | + | 1 | 8-9 | 10-11 | + ------------------------------------------- + +The dorsal scales of cottonmouths are strongly keeled except that those +of the two lower scale-rows on each side are weakly keeled. Also they +are slightly larger than the others. Two apical pits are present on each +dorsal scale. The shape of the scales and number of scale rows vary +depending upon the position on the body. Scales on the neck are +considerably smaller than those elsewhere on the body and are arranged +in two or three more rows than those at mid-body. The skin in the region +of the throat, neck, and fore-body is especially elastic and allows the +swallowing of large prey. Posteriorly from the mid-body the scales +decrease in size and become more angular, those on the tail tending to +be rhomboidal and wider than long. In the region of the anus the number +of scale rows diminishes rapidly, leaving only 12 to 14 rows at the base +of the tail and only three rows immediately ahead of the tail tip. The +tail ends in a spine composed of two scales: one scale covers the +bottom, lower parts of the sides, and tip of the spine; and a shorter +dorsal scale covers the top and upper parts of the sides of the basal +two-thirds of the spine. The spine of embryos and young cottonmouths is +blunt, but is pointed in most adults. + + TABLE 3.--Variation in Numbers of Supralabials and Infralabials + in a Brood of Seven Cottonmouths. + + =========================================== + | Number of | Number of | Number of | + | individuals | supralabials | infralabials | + | 1 | 7 | 9 | + | 1 | 7 | 9-10 | + | 2 | 7-8 | 8-9 | + | 1 | 7-8 | 9 | + | 1 | 8 | 9-10 | + | 1 | 8-9 | 10 | + ------------------------------------------- + + TABLE 4.--Analysis of Number of Scale Rows at Three Parts of + the Body in 81 Cottonmouths. + + ============================================================== + | | Neck | Mid-body | Anterior to anus| + | |--------+--------+--------+--------+--------+--------| + | Number | Number | Per- | Number | Per- | Number | Per- | + | of | of |centage | of |centage | of |centage | + | scales |indivi- | |indivi- | |indivi- | | + |per row | duals | | duals | | duals | | + |--------+--------+--------+--------+--------+--------+--------| + | 29 | 1 | 1.2 | ... | ... | ... | ... | + | 28 | 3 | 3.7 | ... | ... | ... | ... | + | 27 | 52 | 64.2 | ... | ... | ... | ... | + | 26 | 16 | 18.0 | 2 | 2.5 | ... | ... | + | 25 | 8 | 9.9 | 67 | 82.7 | ... | ... | + | 24 | 1 | 1.2 | 4 | 4.9 | ... | ... | + | 23 | ... | ... | 8 | 9.9 | 4 | 4.9 | + | 22 | ... | ... | ... | ... | 4 | 4.9 | + | 21 | ... | ... | ... | ... | 68 | 84.0 | + | 20 | ... | ... | ... | ... | 5 | 6.2 | + -------------------------------------------------------------- + +The number of scale rows on the neck, at mid-body, and just anterior to +the anus is relatively constant at 27-25-21, respectively; but some +individual variation is evident (Table 4). Since the rows are diagonally +arranged, it is necessary in counting scales to proceed either +anteriorly or posteriorly across the back; or the row may be counted in +either direction up to the center of the back and then reversed on the +other side of the snake. In order to count the scale rows in a position +where no scale reduction or addition was occurring and to avoid as much +error as possible, I counted from anterior to center and back on the +neck, in any direction at mid-body, and from posterior to center and +back near the anus. Because females generally are the larger in +circumference posteriorly, they could have more scale rows than males +just anterior to the anus. The few snakes having more than 21 scale rows +in the posterior region offer no conclusive evidence as to tendencies, +but in both instances in which this occurred the females outnumbered the +males three to one. An odd, rather than an even, number of scale rows +occurs on most of the length of the snakes examined, because there is a +mid-dorsal row and scale rows tend to be lost on both sides at about the +same level. An example of scale reduction of one snake was as follows: + + 6+7 (13) 6+7 (96) + 27 -------- 25 -------- 24 -------- 23 --------- 22 --------- + 5+6 (13) 5+6 (90) 7+8 (111) 7+8 (114) + + 6+7 (122) +7, -5 (125) + 23 -------- 22 -------- 23 --------- 21 -------- 22 ------------ + -6 (118) +6 (119) 6+7 (121) +6 (123) + + -6 (126) + 22 -------- 21 (130). + +This scale reduction follows the method proposed by Dowling (1951b: 133) +in which the numbers on the mid-line represent the number of scale rows, +upper figures refer to the right side of the snake, and figures in +parentheses indicate the number of the ventral scale (counted from the +anterior end of the series), thus marking the position of the addition +or reduction. Addition of a row is shown by a plus sign and the number +of the row, whereas reductions are shown by a minus sign and the number +of the row that is lost or by a plus sign between the number of two rows +that join. According to Dowling, variation in number of dorsal scales +characterizes the few genera and species of snakes in which it has been +studied. The time and difficulty involved in ascertaining the number of +scales explain why it has not been widely used in classification. + +[Illustration: FIG. 2. Number of ventral scales in 48 female and 34 +male _A. p. leucostoma_.] + +Ventral scales on 34 males averaged 134.4 (128 to 139), and on 48 +females 133.5 (128 to 137) (Fig. 2.). Barbour (1956:34) found an average +of 135.3 ventral scales on 64 males and 44 females, and Gloyd and Conant +(_loc. cit._) found an average of 134 for both males and females. The +average for the eastern cottonmouth obtained by Gloyd and Conant, +however, was 137 ventrals in both sexes. Some of my counts were made +before I knew of the standard system of counting ventrals proposed by +Dowling (1951a:97-99), in which the first ventral plate is defined as +the most anterior one bordered on both sides by the first row of +dorsals. Therefore, some inconsistencies may exist in my counts. Where +differences occur, Dowling's method probably will indicate the presence +of an additional scale, since it appears to begin farther anteriorly on +the average, than I began counting. + +[Illustration: FIG. 3. Number of caudal scales in 44 female and 34 +male _A. p. leucostoma_.] + + TABLE 5.--Caudal Scale Combinations in 95 Cottonmouths. + U = Undivided; D = Divided. + + ===================================================================== + | Number of scales + |------------------------------------------------------------- + Number | | | | | | | | | | | | | | | | | + of | | | | | | | | | | | | | | | | | + samples| D | U | D | U | D | U | D | U | D |U| D|U| D|U|D|U|D + -------+---+-----+-----+---+----+---+----+---+-----+-+--+-+--+-+-+-+- + 25 | |13-35|10-32| | | | | | | | | | | | | | + 11 |1-2|12-33|14-28| | | | | | | | | | | | | | + 20 | |16-39| 1-9 |1-3|3-24| | | | | | | | | | | | + 20 |1-4| 3-37| 1-21|1-5|1-29| | | | | | | | | | | | + 4 | |14-30| 1-8 |1-7|1-8 |1-4|2-10| | | | | | | | | | + 3 | 1 |18-23| 1-2 |1-2|6-11|1-3|6-9 | | | | | | | | | | + 4 | | 1-17| 1 |1-3|1-8 |1-4|1-3 |1-4|13-22| | | | | | | | + 2 |1-2| 4-16| 1 |1-4| 2 | 1 |1-4 | 1 |18-21| | | | | | | | + 1 | | 20 | 1 | 1 | 1 | 1 | 6 | 1 | 3 |1|11| | | | | | + 1 | | 10 | 2 | 3 | 2 |10 | 1 | 2 | 2 |1| 4|4| | | | | + 1 | | 20 | 1 | 1 | 2 | 1 | 1 | 4 | 4 |2| 4|1| 3| | | | + 1 | 1 | 13 | 1 | 1 | 1 | 3 | 1 | 1 | 1 |4| 2|4|13| | | | + 1 | | 17 | 1 | 1 | 2 | 1 | 1 | 6 | 2 |1| 2|3| 2|7| | | + 1 | | 9 | 1 | 1 | 8 | 1 | 3 | 1 | 1 |3| 1|1| 2|1|1|1|6 + --------------------------------------------------------------------- + +Analysis of caudal scales revealed sexual dimorphism. In the six +specimens from Tennessee, Blanchard (1922:16) found the same thing. +Caudals averaged 45.4 (41 to 50) on 34 males and 42.6 (39 to 49) on 44 +females (Fig. 3). Barbour (_loc. cit._) found an average of 45.7 (30 to +54) caudals in males and 43 (17 to 56) in females. Caudal scale counts +by Gloyd and Conant (_loc. cit._) averaged 44 (38 to 49) in males and 42 +(37 to 48) in females of _leucostoma_; in _piscivorus_ they averaged 48 +(42 to 53) in males and 44 (41 to 49) in females. Another +seldom-mentioned, unusual characteristic of the caudal scales of +copperheads and cottonmouths is that some are single (usually those at +the base of the tail) and others divided (Table 5). To my knowledge, all +other species have either single or divided scales the entire length of +the tail. See Klauber (1941:73) and Fox (1948:252) concerning +correlation of few scales with warm environment. + + +Dentition + +Cottonmouths, like other pit-vipers, have their teeth reduced in number +and have enlarged, highly specialized fangs. Small teeth occur on the +palatine and the pterygoid in the upper jaw and on the dentary in the +lower jaw. The dentary bone bears 17 curved teeth that decrease in size +posteriorly. The palatine bears five small, strongly curved teeth, and +the pterygoid bears 16 to 18 strongly curved teeth decreasing in size +posteriorly. The numbers of teeth mentioned above in each instance refer +to the number of sockets rather than the actual number of teeth, because +teeth are frequently shed, leaving some of the sockets empty at any one +time. + +The maxillary bone has two sockets side by side which bear the poison +fangs, usually one at a time. During the period shortly before a fang is +to be shed, however, its replacement becomes attached in the alternate +socket; and both fangs may be functional for a short time. The old fang +then becomes weakened at its base, eventually breaks off, and is +swallowed. At any one time four or five replacement fangs in various +stages of development are found in the gum behind the functional fang. +These replacement fangs, which are arranged in alternate rows, gradually +enlarge as they move forward in their development and, in juveniles, are +generally slightly longer than the fangs that they replace. + +In 1963 I examined the fangs of 14 cottonmouths at four- to seven-day +intervals for a period of six weeks. The fang-shedding cycle was found +to be highly irregular, with a double condition (on one or both sides) +occurring one-third of the time. Approximately the same proportion of +double fangs was found in preserved individuals. A replacement period of +at least five days was observed in one snake. One-half the cycle (from +replacement on one side to replacement on the other) varied from five to +twenty days, indicating that the cycles for each fang are independent of +one another. Bogert (1943:324) found that young rattlesnakes are born +with functional fangs in the two inner sockets. Nonsynchronous use of +the sockets on opposite sides of the head in rattlesnakes is a later +development which results from accidents or other conditions leading to +a longer retention of the fang on one side than on the other (Klauber, +1956:723). I found a double set of fangs in cottonmouths only twice in +the six-week period. A complete cycle was recorded in ten instances in a +period of 19 to 23 days and in two instances in 32 days. One cottonmouth +was examined periodically over a 34-day period by Allen and Swindell +(1948:12), but a complete fang-shedding cycle was not observed. Fitch +(1960:110) reported a 33-day cycle in copperheads; Klauber (1956:726) +estimated the normal active life of each fang of an adult rattlesnake to +be from six to ten weeks, but he made no observations to confirm his +estimation. + +Fangs measured from the tip of the notch of the basal lumen to the end +of the fang vary from about 1.3 per cent of the snout-vent length in +juveniles to about 1.0 per cent in large adults (Table 6). The fangs are +longer than those of copperheads (Fitch, 1960:111). Klauber's (1956:736) +figures on fang-lengths in all species of rattlesnakes are percentages +of total length rather than of the snout-vent length. The fangs of +various species of rattlesnakes range from nearly the same proportionate +length as those of cottonmouths to some much longer. + +From patterns of bites of venomous snakes, Pope and Perkins +(1944:333-335) attempted to correlate number, size, and patterns of +tooth marks with size and generic identity of the snake responsible for +the bite. Distance between fangs is relatively constant for snakes of a +particular size (Table 6) regardless of genus, but the fangs of a +cottonmouth are directed outward to variable degrees, and puncture +wounds could easily resemble those of a much larger snake (Table 7). +Also there is no direct relationship between size of snake and toxicity +or amount of venom injected. Consequently information of this kind is of +little or no value from a medical standpoint. + + TABLE 6.--Correlation of Relative Fang-length and Distance + Between Fangs at Base with Snout-vent Length of Cottonmouths. + + ======================================================= + |Snout-vent |Number |Average |Number |Average | + |length |in |ratio of |in |ratio of | + |(millimeters) |sample |fang-length |sample |distance | + | | |to | |between | + | | |snout-vent | |fangs to | + | | |length | |snout-vent | + | | |(percent) | |length | + | | | | |(percent) | + |--------------+-------+------------+-------+-----------| + | 200-299 | 3 | 1.33 | 3 | 2.57 | + | 300-399 | 7 | 1.30 | 5 | 2.48 | + | 400-499 | 13 | 1.21 | 9 | 2.21 | + | 500-599 | 12 | 1.22 | 8 | 2.19 | + | 600-699 | 7 | 1.17 | 1 | 2.10 | + | 700-799 | 5 | 1.07 | 4 | 1.65 | + | 800-899 | 1 | 1.00 | 1 | 2.00 | + ------------------------------------------------------- + + TABLE 7.--Contrast in Measurements Between the Base of the + Fangs and Between Fang Punctures of Nine Cottonmouths (in + millimeters). + + ================================================== + | Distance between | Distance between | Snout-vent | + | base of fangs | fang punctures | length | + |------------------+------------------+------------| + | 7.7 | 13.0 | 400 | + | 8.7 | 14.0 | 575 | + | 10.0 | 22.5 | 526 | + | 11.0 | 18.0-19.0 | 590 | + | 12.0 | 18.0 | 793 | + | 13.0 | 17.0, 20.0 | 558, 612 | + | 15.5 | 23.5 | 800 | + | 16.0 | 24.0 | 800 | + -------------------------------------------------- + + + + +HABITAT AND LIMITING FACTORS + + +Although usually associated with swamps and lowlands along river +bottoms, the cottonmouth lives in a variety of habitats ranging from +salt marshes to cool, clear streams and from sea level to an altitude of +2300 feet. Shaded, moist areas either in or beside shallow waters are +preferred, but cottonmouths occasionally wander as far as a mile from +water. + +In the pine-oak forests of Nacogdoches County in eastern Texas +cottonmouths and copperheads are probably the most abundant species of +snakes. Specimens have been collected near Nacogdoches in ponds, swamps, +clear and fast-running streams with rock bottoms, and sluggish muddy +streams. On the Stephen F. Austin Experimental Forest numerous +cottonmouths live in a swamp until around mid-July, when it becomes dry. +A small stream west of the swamp seems to be used as a migration route +to and from the swamp. Slightly more than a mile downstream cottonmouths +are common in a bottomland area. The ground is always moist and no +undergrowth occurs; a few small clear springs produce shallow trickles +that run into a swamp. Cottonmouths can often be found here, lying in or +beside the small trickles. + +I have seen cottonmouths in various types of aquatic habitats in +Brazoria County. In most places in this area, cottonmouths are found in +association with one or more species of water-snakes (including _Natrix +cyclopion_, _N. erythrogaster_, _N. rhombifera_, and _N. confluens_), +which greatly outnumber the cottonmouth. Interspecific competition may +be reduced somewhat by cottonmouths sometimes feeding on water-snakes. + +The numerous statements in the literature concerning the habitat of the +cottonmouth can be summarized most easily by the following short +quotations: + + _Agkistrodon piscivorus piscivorus_--"Marshes and lakes; ponds + and streams with wooded shores; low country near water; + roadside ponds; drainage ditches; coastal 'banks'; keys; some + Gulf coast islands; mangrove swamps." (Wright and Wright, + 1957:919.) + + _Agkistrodon piscivorus leucostoma_--"Cypress, gum, river + swamps; alluvial swamps wooded or not wooded; water courses of + the south such as rivers, bayous, backwaters of small branches; + hill streams in the north; ... marshy places in prairies ... + rice fields, bottomland pools; margins of above habitats, + pools, shallow lakes, swampy places, temporary flood lands.... + In, under, or on fallen timber, in holes in banks, rocky + bluffs, crayfish burrows. In short it is very aquatic." (Wright + and Wright, _op. cit._:923.) + +Geographically cottonmouths differ somewhat in their ecological +requirements, but are basically much alike in most respects. The areas +of greatest abundance are those having 40 inches or more of annual +rainfall. The northern edge of the range has a mean temperature of +approximately 38° F. in January in Virginia and 30° F. in Missouri, +although the lowest temperature reached in these areas is more important +as a limiting factor. The annual rainfall in both Virginia and Missouri +amounts to approximately 40 inches. Moisture, as well as temperature, +may play an important role in the northward distribution of the species. +The eastern cottonmouth seems to be less tolerant of low temperatures +than the western subspecies. Mean January temperatures equal to those +along the northern limits of the western cottonmouth's distribution are +reached in the vicinity of Connecticut, which is north of the geographic +range of the eastern subspecies. + +The depths to which cottonmouths penetrate into their dens may have a +limiting influence upon the geographic range, especially in the northern +extremes. Bailey (1948:215) discussed the possibility that populations +of snakes may be significantly depressed because of winter kill of +individuals that "hibernate" at shallow depths. He speculated also that +the short growing season does not allow enough time for the essentials +of existence to be carried out, and the prolonged period of inactivity +overtaxes the energy reserve of the species. + +Available food does not seem to be of much importance as a limiting +factor, for the cottonmouth is remarkably indiscriminate in its choice +of prey, feeding upon almost any vertebrate animal that happens to come +within reach. Competition for food, however, may play an important role. + + + + +REPRODUCTION + +Courtship and Mating + + +A review of available literature indicates no records of courtship of +the cottonmouth other than statements that breeding occurs in early +spring. In a close relative, the copperhead (see Fitch, 1960:159-160), +mating occurs almost any time in the season of activity but is mainly +concentrated in the few weeks after spring emergence, at about the time +when females are ovulating. Klauber (1956:692) concluded that along the +southern border of the United States rattlesnakes normally mate in +spring soon after coming out of their winter retreats; but farther north +where broods are produced biennially, the mating times may be more +widely dispersed, and summer and fall matings may even predominate. + +The only record of copulation in the cottonmouth was reported by Allen +and Swindell (1948:11), who observed a pair copulating for three hours +on October 19, 1946, at the Ross Allen Reptile Institute. Davis +(1936:267-268) stated that courtship in cottonmouths is violent and +prolonged but did not note any nervous, jerky motions or nudging of the +female along her back and sides as had been observed in other genera of +snakes. Carr (1936:90) saw a male cottonmouth seize a female in his +mouth and hold her, but no courtship followed. + + +Reproductive Cycles + +Many persons have assumed that gestation periods in snakes are the +intervals between mating and parturition, and that mating and ovulation +occur at approximately the same time. However, retention of spermatozoa +and delayed fertilization indicate that copulation is not a stimulus for +ovulation. + +A biennial reproductive cycle was found for the copperhead in Kansas +(Fitch, 1960:162), the prairie rattler in Wyoming (Rahn, 1942:239) and +in South Dakota (Klauber, 1956:688), the great basin rattler in Utah +(Glissmeyer, 1951:24), and the western diamondback rattler in +northwestern Texas (Tinkle, 1962:309). Klauber's (1956:687) belief that +the reproductive cycle of rattlesnakes varies with climate, being +biennial in the north and annual in the south, is supported by similar +climatic variation in the reproductive cycle of the European viper which +was discussed by Volsøe (1944:18, 149). + +If data for a large number of females were arranged as are those in +Table 8, they might reveal whether the breeding cycle is annual or +biennial. The figures presented in Table 8 are misleading if viewed +separately because of the small number of individuals included in some +of the size classes. + +The smallest reproductive female found measured 455 millimeters in +snout-vent length. Conant (1933:43) reported that a female raised in +captivity gave birth to two young at an age of two years and ten months. +The size classes represented by gravid females found by Barbour +(1956:38) in Kentucky indicate that breeding occurs at least by the +third year. + +The ovaries of female cottonmouths examined revealed ova in various +stages of development. In individuals less than 300 millimeters in +snout-vent length the ovaries are almost completely undeveloped; in +immature individuals from 300 to 450 millimeters in length the follicles +are from one to two millimeters in length; in post-post females +follicles vary in size, the largest being about seven millimeters. +Reproductive females also contain follicles of various sizes. One or two +sets are less than three millimeters in length, and large ova that soon +are to be ovulated are present. Ovarian ova found in April ranged in +length from 23 to 35 millimeters. No embryonic development was observed +in most individuals until June or later. + + TABLE 8.--Percentage of Gravid Females of _A. p. leucostoma_ in + 50 Millimeter Size Classes. + + ===================================== + |Snout-vent |Number |Total |Percentage| + | | of |number| | + | length |gravid | in | gravid | + | |females| size | | + | | |class | | + |-----------+-------+------+----------| + | 450-499 | 3 | 14 | 21.4 | + | 500-549 | 7 | 17 | 41.2 | + | 550-599 | 8 | 17 | 47.1 | + | 600-649 | 5 | 7 | 71.4 | + | 650-699 | 2 | 9 | 22.2 | + | 700-749 | 2 | 3 | 66.7 | + | 750-799 | 1 | 1 | 100.0 | + | 850-899 | 1 | 1 | 100.0 | + | Totals | 29 | 69 | 42.0 | + ------------------------------------- + +Increase in length of testes appears to be correlated with length of the +individual rather than cyclic reproductive periods (Fig. 4). + +The reproductive cycle in cottonmouths resembles that illustrated by +Rahn (_op. cit._:237), in which the ovarian follicles of post-partum +females begin to enlarge in late summer and autumn, with ovulation +occurring the following spring. By means of retaining sperm successive +broods possibly are produced after only one mating. In captivity, at +least, some females may not follow this biennial cycle; Stanley Roth +(M.S.), biology teacher in high school at Lawrence, Kansas, had a female +of _A. p. piscivorus_, from Florida, that produced broods of 14 and 12 +young in two consecutive years. + +[Illustration: FIG. 4. Length of testes in cottonmouths of various +sizes (·--left; º--right). The right testis is always longer than +the left.] + + +Embryonic Development + +After ova are fertilized a three and one-half to four-month period of +development begins which varies somewhat depending on the temperature. +In almost every instance the ova in the right uterus outnumber those in +the left. Embryos usually assume the serpentine form in the latter part +of June and are coiled in a counterclockwise spiral with the head on the +outside of the coil. At this time the head is relatively large and +birdlike in appearance with conspicuous protruding eyes. Sex is easily +noted because the hemipenes of males are everted. By late July scales +are well developed and the embryo is more snakelike in appearance, but +pigmentation is still absent. By mid-August the color and pattern are +well developed, the egg tooth is present, the snake shows a considerable +increase in size over that of the previous month, and much of the yolk +has been consumed. Some females that contain well developed embryos also +contain eggs that fail to develop. Sizes of ova vary irrespective of +size of female and stage of embryonic development. Lengths of ova ranged +from 22 to 51 millimeters in May to 35 to 49 millimeters in July and +August. A two-yolked egg was found in one female. + + +Birth of Young + +Accounts in the literature of 15 litters of cottonmouths fix the time of +birth as August and September. Conant (1933:43) reported the birth of a +litter in mid-July by a female that had been raised in captivity, and +one female that I had kept in captivity for two months gave birth to a +litter between October 19 and October 25. The conditions of captivity +undoubtedly affected the time of birth in both instances. + +Wharton (1960:125-126) reported the birth and behavior of a brood of +seven cottonmouths in Florida. I was given notes of a similar nature by +Richard S. Funk of Junction City, Kansas, on a brood of five +cottonmouths. The mother of the brood was caught in June, 1962, in +Tarrant County, Texas, by Richard E. Smith, and was 705 millimeters in +snout-vent length. The first young was found dead in an extended +position a few inches from the fetal membranes at 11:05 p.m. on August +22. The second young was born at 11:07 p.m. The intervals between the +successive births were three, seven, and four minutes; and time until +the sac was ruptured in each instance was six, five, eight, and 11 +minutes. The time interval between the rupture of the sac and emergence +of each individual was 41, 92, 154, and 34 minutes. The mother's actions +in giving birth to the last four young were essentially as described by +Wharton (_loc. cit._), except that the intervals between successive +births did not increase. Within one minute after rupturing the sac and +while its head was protruding, each of the four living young opened its +mouth widely from three to seven times, then took its first breath. +Breaths for the first three hours were steady at three or four per +minute but then decreased to two or three per minute. Pulse rate for the +four averaged 38 per minute while at rest but increased to 44 per minute +after voluntarily crawling. + + +Number of Young per Litter + +Records of from one to 16 young per litter have been reported (Ditmars, +1945:330; Clark, 1949:259), but the average is probably between six or +seven. Most accounts in the literature present information on number of +ova or embryos per female rather than the number of young. Size and age +of the mother (Table 9) influence the number of ova produced. Allen and +Swindell (1948:11) recorded three to 12 embryos in 31 cottonmouths +varying in total length from 26 to 44 inches. An average of 6.5 embryos +per female was found. + + TABLE 9.--Number of Ova Produced by Fecund Cottonmouths. + + ====================+============+====================== + Snout-vent length | Number | Number of ova, + in millimeters | in sample | average and extremes + --------------------+------------+---------------------- + 450-549 | 10 | 4.1 (2 to 7) + 550-649 | 11 | 4.9 (1 to 8) + 650-749 | 4 | 6.3 (4 to 8) + 750-849 | 1 | 5 + 850-949 | 1 | 14 + -------------------------------------------------------- + +Mortality at birth has been recorded for almost every litter born in +captivity (see Allen and Swindell, _loc. cit._; Conant, 1933:43; +Wharton, 1960:125). A female that I kept in captivity gave birth to +seven young. Three never ruptured their sacs, and another died soon +after leaving the sac. The effects of captivity on females may result in +higher rates of deformity and mortality in young than is common in +nature. Klauber (1956:699-700) estimated that the defects brought about +by conditions of captivity on rattlesnakes eliminate about three young +per litter. + + +Population Composition + +No investigator has yet analyzed the composition of a population of +cottonmouths according to age, sex and snout-vent length. Barbour +(1956:35) did sort 167 snakes into size classes, but did not determine +sex ratio, size at sexual maturity, reproductive cycles, or snout-vent +length. He recorded total lengths from which snout-vent lengths cannot +be computed because of differential growth rates and different bodily +proportions of the two sexes. I judge from my findings that he included +immature individuals in his three smallest size classes (45.5 per cent +of the population). I found at least 32.5 per cent immature individuals +(Fig. 5) in my material, but it was not a natural population. + +The sex ratios of several small collections from natural populations +varied, and no conclusions could be drawn. Females comprised 53 per cent +of the specimens included in Fig. 5 and in a group of 48 embryos which +represented eight broods. That percentage may not be the percentage in a +natural population but is used in making assumptions because I lack +better information. + + +Reproductive Potential + +If data in Fig. 5 are representative of a natural population and if 61 +per cent of the females are sexually mature, the reproductive potential +can be estimated as follows: assuming a cohort of 1000 cottonmouths +contains 530 females, 61 per cent of the females (323 individuals) +probably are adults. If 42 per cent of these females produce 6.5 young +per female in any season (Tables 8 and 9), 136 females will produce 884 +young. But if 50 per cent of the adult females are reproductive (as +would be assumed if reproduction is biennial), 1050 young will be +produced. Actually the number of young required per year to sustain a +population is unknown, because mortality rates at any age are unknown. + +[Illustration: FIG. 5. Composition of a group of cottonmouths examined +in this study. Individuals less than 450 millimeters in snout-vent +length are considered as immature. Specimens from 200 to 249 millimeters +in length are included in the 200-millimeter class, _etc._] + + + + +GROWTH AND DEVELOPMENT + +Size at Birth and Early Growth + + +Size at birth depends on the health of the mother. According to Fitch +(1960:182), many litters of copperheads born in captivity are stunted. +Seven young cottonmouths (two males and five females) born in captivity +were each 185 millimeters in snout-vent length and 40 millimeters in +tail length. Weights of the three living young were 10.0, 10.1, and 11.1 +grams. Another litter of five young measured by Richard S. Funk were +larger, and differences in the proportions of the tail length and +snout-vent length suggest the sexual dimorphism found in larger +individuals. However, sex of these young snakes was not recorded. +Snout-vent length and tail length in millimeters were 232, 41; 243, 47; +229, 40; 240, 48; and 225, 40 in the order of their birth. These snakes +are considerably smaller than the nine young of _A. p. piscivorus_ +reported by Wharton (1960:127) that averaged 338 millimeters total +length and 28.7 grams. The yolk of one young _piscivorus_ was 11.7 per +cent of the total weight. Yolk is used up in about two weeks if its rate +of utilization resembles that of the copperhead as reported by Gloyd +(1934:600). + +Early rates of growth of three living young are shown in Table 10. On +the 56th day after birth, each was fed one minnow less than two inches +long. Between the 80th and 120th days three additional small minnows +were fed to each snake. Young cottonmouths increase nearly 50 +millimeters in length by the first spring if they inhabit warm areas and +feed in autumn or winter. + +Variation in size of newborn cottonmouths may be less in nature than in +captivity. Average size at birth can be determined accurately by the +size of young captured in early spring, at least in northern parts of +the range where winter feeding and growth do not occur at all or are +negligible. Total lengths of 19 juveniles thought by Barbour (1956:38) +to be seven to eight months old do not differ markedly from lengths of +the five newly-born young measured by Funk. + + TABLE 10.--Rate of Growth of Three Young Cottonmouths. + + ========+================================================= + | | Snout-vent length/tail length--weight in grams | + | Age +----------------+----------------+----------------| + |in days | Female No. 1 | Female No. 2 | Male | + |--------+----------------+----------------+----------------| + | 2 | 185/40--11.1 | 185/40--10.1 | 185/40--10.0 | + | 7 | 192/40-- | 190/40-- | 189/40-- | + | 22 | 195/40--10.3 | 200/41.5--10.6 | 197/40-- | + | 80 | 204/40--11.7 | 203/42--10.4 | 218/48--14.3 | + | 88 | .... | 204/44-- | .... | + | 143 | 215/40.5--13.3 | .... | 225/48--15.1 | + --------+----------------+----------------+---------------- + + +The Umbilical Scar + +The umbilical cord is broken at birth and the navel closes within a few +days; but the scar, involving from two to four ventral scales, remains +throughout life. Position of the scar was found by Edgren (1951:1) to be +sexually dimorphic in the eastern hog-nose snake (_Heterodon +platyrhinos_), but nothing has been published on this matter concerning +the cottonmouth. Consequently, I counted the scales of several +individuals from the anal plate, and there was no marked difference in +the position of the scar in males and females; it varied in position +from the 10th to the 18th scale. When counted from the anterior end, the +scar ranged from ventral number 115 to 122 (average, 119) in 28 females +and from number 117 to 126 (average, 121) in 14 males. The difference +between male and female cottonmouths is not nearly so great as in +_Heterodon_. + + +Later Growth and Bodily Proportions + +The only records of growth increments in a natural population of +cottonmouths are those in Table 11. The period of growth is mostly the +period of activity, and differences are expected between northern and +southern populations. As size increases, determination of growth rate +becomes more difficult because age classes overlap in size. Growth of +any individual depends not only on climate and food but also on disease +and parasitism and the innate size potential. Stabler (1951:91) showed +weight and length relationships in two cottonmouths for a period of six +and one-half years. + + TABLE 11.--Growth Increments in Cottonmouths (Barbour, + 1956:38-39). + + ============================================= + | Number of | Total |Estimated| Estimated | + | | length | age | growth | + | | | | from | + | | | | preceding | + | | | | year | + |individuals| in |in months| in | + | |millimeters| |millimeters| + |-----------+-----------+---------+-----------| + | 19 | 260-298 | 7-8 | 25 | + | 11 | 312-337 | 19-20 | 45 | + | 40 | 355-485 | 31-32 | 95± | + | 83 | 500-1000 | 43-44+ | ? | + --------------------------------------------- + +My study failed to reveal any secondary sexual difference in growth rate +and maximum size. Of the 306 cottonmouths measured by me, 16 males and +five females exceeded 700 millimeters in snout-vent length. Two males +were more than 850 millimeters long. One cottonmouth lived in captivity +for 18 years and 11 months (Perkins, 1955:262). The maximum total +lengths were reported by Conant (1958:186-187) to be 74 inches (1876 +mm.) in _A. p. piscivorus_ and 54 inches (1370 mm.) in _A. p. +leucostoma_. + +[Illustration: FIG. 6. Head length (º) and head width (·) expressed as a +percentage of snout-vent length of living and preserved cottonmouths. +Head length was measured from the tip of the snout to the posterior end +of the mandible. Head width was measured across the supraocular scales, +since accuracy was greater than if measured at the posterior edge of the +jaw. No sexual dimorphism or geographical variation occurs in these +characters.] + +Proportions of various parts of the body vary considerably depending on +age, size and, in some instances, sex. Heads are proportionately larger +in young than in adults (Fig. 6), as is true of vertebrates in general. +This larger head has survival value for the cottonmouth in permitting +more venom to be produced and in permitting it to be injected deeper +than would be the case if the proportions were the same as in adults. +Relative to the remainder of the snake the head is considerably larger +than in the copperhead (Fitch, 1960:108) and slightly larger than in the +rattlesnake, _Crotalus ruber_ (Klauber, 1956:152). + +[Illustration: FIG. 7. Tail length expressed as a percentage of +snout-vent length of living and preserved cottonmouths (·--males; +º--females).] + +In general, tails are relatively longer in males than in females of the +same size (Fig. 7), except that there is little or no difference at +birth. Growth of the tail in males proceeds at a more rapid rate. In +certain individuals sex cannot be recognized from length of the tail +relative to snout-vent length because overlapping occurs, especially in +medium-sized individuals. Similar changes of proportions with increase +in age occur in copperheads (Fitch, 1960:106) and rattlesnakes (Klauber, +1956:158-159), but the tail of the cottonmouth is relatively much +longer. + + + + +SHEDDING + +The Shedding Operation + + +Shedding of the skin is necessary to provide for growth and wear in +snakes. The milkiness or bluing of the eyes, which causes partial +blindness, marks the initial stage of shedding and is caused by a +discharge of the exuvial glands that loosens the old _stratum corneum_ +from the layer below. In four to seven days the opaqueness disappears, +and the snake sheds after an additional three to six days (Table 12). +Young snakes first shed within a few days after birth and generally shed +more frequently than adults, but the interval is variable. The eyes of +three young cottonmouths observed by Wharton (1960:126) became milky on +the fourth day but cleared on the seventh day, and the skin was shed on +the eighth day. The eyes of three young kept by me became milky two to +three days after birth, cleared on the seventh to tenth days, and the +skin was shed on the thirteenth day. Possibly the relatively long +interval in this instance resulted from low relative humidity in the +room where the snakes were kept. According to Fitch (1960:134), litters +of young copperheads usually shed within three to ten days after birth; +but under unusually dry conditions shedding did not occur for several +weeks. + + TABLE 12.--Duration of Preparatory Period (in days) to Shedding + in 11 Cottonmouths. + + ============================== + |Duration | Time |Time from | + | of |between |beginning | + |cloudiness|clearing| of | + | | and |cloudiness| + |of eyes |shedding| until | + | | | shedding | + |----------+--------+----------| + | 5 | 6 | 11 | + | 7 | 3 | 10 | + | - | - | 6 | + | - | - | 6 | + | 5 | 3 | 8 | + | 4 | 6 | 10 | + | 7 | 3 | 10 | + | 5 | 6 | 11 | + | 5 | 3 | 8 | + | 7 | - | - | + | 7 | 3 | 10 | + | ---- | ----| ---- | + |[=X] 5.4 |[=X] 3.8| [=X] 9.0 | + ------------------------------ + +Cottonmouths as well as other snakes usually do not feed until after the +skin is shed and are generally quiescent during the period preceding +shedding, except that immediately before shedding they become active and +rub their snouts on some rough object and may yawn several times +seemingly in an attempt to loosen the skin along the edges of the lips. +After the skin is loosened from the head, more rubbing against rough +surfaces and writhing serves to pull the old skin off, turning it inside +out. Once the old skin has passed over the thick mid-body, the snake +often crawls forward using rectilinear locomotion until the skin is +completely shed. It normally comes off in one piece; but, if the snake +is unhealthy or has not had sufficient food or water, the skin may come +off in patches. Frequently one or both of the lens coverings are not +shed immediately and impair the sight. Bathing or swimming ordinarily +causes dried skin to peel off; and, because of the cottonmouth's aquatic +habits, its chances of shedding successfully are much greater than those +of less aquatic snakes. Cottonmouths that have recently shed have bright +and glossy patterns, in contrast to the dull and dark appearance of +those that are preparing to shed. + + +Frequency of Shedding + +Most of our knowledge concerning the frequency of shedding is based upon +observations of captives. It is known that the intervals between +exuviations are largely dependent upon the amount of food taken and the +rate of growth. Unless laboratory conditions closely resemble those in +the field, shedding frequencies in captives probably differ much from +those of free-living snakes. + +Only two of my captives shed twice. The intervals between exuviations in +the two snakes were eight and five months, lasting from August to April +and from December to May, respectively. Ten other snakes shed once in +the period from January through July. Stabler (1951:91) presented data +concerning shedding of two cottonmouths kept 12 and 14 years in +captivity. One shed 25 times in 12 years and the other shed 37 times in +14 years, giving an average of 2.1 and 2.6 per year, respectively. +Neither of the snakes shed from December through March, but the period +of shedding corresponded to the period of greatest activity and growth. +In Florida, cottonmouths shed four to six times a year, according to +rate of growth (Allen and Swindell, 1948:7). + + + + +FOOD HABITS + +Methods of Obtaining Prey + + +Food is obtained by a variety of methods depending on the type of food, +age of the cottonmouth, and possibly other factors. Some captives lie in +ambush and others crawl slowly in active search. At the first cue of +possible prey, either by sight, scent, or differential temperature +detection by the pit, the snake appears to become alert and flicks its +tongue out at fairly rapid intervals. + +By means of the facial or loreal pit found in all crotalids, the snake +is able to detect objects having temperatures different from that of the +surroundings of the objects. In detecting prey the tongue acts to +sharpen the sense of "smell" by conveying particles to Jacobson's organs +in the roof of the mouth. On many occasions cottonmouths appeared to +rely solely on sight; they passed within a few inches of prey, +apparently unaware of its presence until it moved. When pools of water +begin to dry up toward the end of summer, cottonmouths often congregate +and feed on dying fish. In these instances the fish are usually taken as +they come to the surface. In laboratory observations moccasins seize +live fish and some moccasins carry the fish until they have received +lethal doses of venom; afterward the fish are swallowed. But grasping +and manipulation of the prey occurs without the fangs' being employed, +especially in the case of dead fish. On one occasion a cottonmouth was +observed to grasp the edge of a glass dish that had contained fish and +apparently retained the odor. On another occasion I placed several fish +in a bowl, rubbed a stick on the fish, and then touched each snake +lightly on the nose with the stick. The snakes crawled directly to the +bowl and began feeding. At other times these same snakes crawled around +the cage in an apparent attempt to locate the food but paid little +attention to fish held in front of them. If the catching of prey under +natural conditions were as uncoordinated as it sometimes is in +captivity, the snakes probably would not be able to survive. + +Wharton (1960:127-129) described tail-luring in one individual of a +76-day-old brood of cottonmouths. The snake lay loosely coiled with the +tail held about six centimeters from the ground; a constant waving +motion passed posteriorly through the terminal inch of the tail. These +movements ceased at 7:20 p.m. but were resumed at 7:40 a.m. the +following day. All observations were under artificial light. The "caudal +lure" as a means of obtaining prey has been described in other species +and related genera by Neill (1960:194) and Ditmars (1915:424). + +Various authors have suggested that the method of capture differs +according to the kind of prey. Allen and Swindell (1948:5) stated that +cottonmouths retain their hold after striking fish or frogs but will +release a mouse after delivering a bite and are timid in striking at +larger rodents. Neill (1947:203) noted that a cottonmouth always waited +several minutes after biting a large rat before approaching its prey. +This same type of behavior has been reported for copperheads (Fitch, +1960:194) and rattlesnakes (Klauber, 1956:618). Cottonmouths observed by +me retained a strong hold on fish, frogs, and sometimes mice, but almost +always released large mice and baby chicks, which were not eaten until +after death. + +Different behavior according to type of prey is correlated with ability +of prey to retaliate, although some animals may not be released because +they could easily escape. For instance, a frog could hop far enough to +escape in a matter of seconds if released. A 73-millimeter _Rana +pipiens_ that I observed was bitten twice within one and a quarter hours +and died 45 minutes after the last bite. Its movement was uncoordinated +by the time of the second bite, but it could have escaped had the frog +not been confined. Although it is doubtful that normal, healthy fish are +frequently captured by cottonmouths, Allen (1932:17) reported that a +cottonmouth was seen pushing a small, dead pike about on the surface of +a stream. A wound on the belly of the fish indicated that it had been +bitten. A 17-gram creek chub (_Semotilus_) and a 13.7-gram bass +(_Micropterus_) were injected by me with one-fourth cubic centimeter of +fresh venom near the base of the tail in order to determine whether the +fish could escape after being bitten and released. The creek chub +flipped onto its back after a minute and 45 seconds and gill movements +stopped in eight minutes and 35 seconds; the bass flipped over after 50 +seconds and died in two minutes and 10 seconds. The venom immediately +affected both fish, and it is unlikely that either could have swum more +than a few feet. + +After its prey has been killed, a cottonmouth examines the body from end +to end by touching it with the tongue. Then the animal is grasped in the +mouth without the use of the fangs and is slowly manipulated until one +end (usually the head) is held in the mouth. The lengthy process of +swallowing then takes place, the fangs and lower jaws alternately +pushing the prey down the throat. + + +Food and Food Preferences + +The cottonmouth seems to be an opportunistic omni-carnivore, because it +eats almost any type of flesh that is available, including carrion. It +feeds primarily upon vertebrates found in or near water; but +invertebrates and eggs have also been found in the diet. The only +potential prey items that seem not to be normally eaten are bufonid +toads and tadpoles. I have occasionally offered tadpoles and frogs to +cottonmouths, but only the frogs were accepted. But, Stanley Roth kept a +cottonmouth in captivity that ate both toads and tadpoles. If tadpoles +are commonly eaten, their probable rapid digestion would make +identification almost impossible. + +Following is a list of known foods of the cottonmouth: + + Captivity: "... rattlesnake.... The same moccasin also killed + and ate a smaller snake of its own species...." (Conant, + 1934:382.) + + Florida: "3 heron feathers, bird bone, _Eumeces inexpectatus_, + 3 fish all under one inch in length, 1 heron egg shell" (Carr, + 1936:89). According to Allen and Swindell (1948:5), "the food + included other moccasins, prairie rattlesnakes, king-snakes, + black snakes, water snakes, garter snakes, ribbon snakes, and + horn snakes ... most of the species of frogs, baby alligators, + mice, rats, guinea pigs, young rabbits, birds, bats, squirrels, + and lizards ... a mud turtle ... a case of a four footer eating + ten to twelve chicken eggs. The most common food appears to be + fish and frogs. Catfish are included on this list...." Yerger + (1953:115) mentions "an adult yellow bullhead, _Ameiurus + natalis_ ... 306 mm. in standard length [from a 63-inch + cottonmouth]." + + Georgia: "... full grown _Rana catesbeiana_, several foot-long + pickerel ... dead fish if placed in a pan of water.... _Natrix + sipedon fasciata_ and _Masticophis flagellum_ ... rats.... + Toads and large _Eumeces laticeps_ were always ignored." + (Neill, 1947:203.) "_Natrix_, _Heterodon_, _Kinosternon_, + _Rana_, _Hyla cinerea_, _Microhyla_, Microtine [_Pitymys + pinetorum_]." (Hamilton and Pollack, 1955:3.) + + Mississippi: "... _Hyla gratiosa_.... In captivity specimens + have eaten frogs, mice, birds, dead fish, pigmy rattlers and + copperheads. Toads ... were refused" (Allen, 1932:17). One + moccasin "disgorged a smaller decapitated moccasin ... killed + the day before by boys" (Smith and List, 1955:123). + + Tennessee: "Beetles in one stomach; lizard (_Eumeces_) in + another stomach; small snake (_Natrix_) in one intestine, and + hair in another intestine. One stomach contained numerous bits + of wood, up to four inches in length...." (Goodman, 1958:149.) + + Kentucky: "_Siren intermedia_ was the most abundant food item + in both volume and occurrence. Frogs of the genus _Rana_ ranked + second. Together, these two items comprised almost 2/3 of the + food of the snakes. The other food items were distributed among + the fishes, reptiles, and other amphibians [one _Rana_ tadpole + included]." (Based on 42 samples--Barbour, 1956:37.) + + Illinois: (Based on 84 samples--Klimstra, 1959:5.) + + _Per cent Frequency_ _Per cent_ + _Food Item_ _of Occurrence_ _Volume_ + + Pisces 39.3 31.9 + Amphibia 36.9 26.0 + Reptilia 25.0 18.2 + Mammalia 30.9 17.9 + Gastropoda 17.8 1.0 + Miscellaneous 25.0 5.0 + (Algae, Arachnida, + Aves, Insecta) + + Louisiana: Penn (1943:59) mentions that a "female had just + eaten two young cottonmouths...." Clark (1949:259) mentions + "100 specimens--34 fish; 25 _Rana pipiens_; 16 _Rana + clamitans_; 7 _Acris_; 4 _Natrix sipedon confluens_; 8 birds; 5 + squirrels ... catfish thirteen and one-half inches in length + ... small-mouth black bass [eleven inches]." + + Oklahoma: Force (1930:37) remarks that the moccasin "eats + bullfrogs ... but refuses leopard frogs." Trowbridge (1937:299) + writes: "several sun perch.... Another had eaten six catfish + six to ten inches long ... a water snake (_Natrix s. + transversa_) about 18 inches long ... frogs, mostly _Rana + sphenocephala_." Carpenter (1958:115) mentions "a juvenile + woodthrush.... Seven last instar cicadas ... a young + cottontail." According to Laughlin (1959:84), one moccasin + "contained the following items: 18 contour feathers of a duck, + probably a teal; one juvenile cooter turtle, _Pseudemys + floridana_; and a large mass of odd-looking unidentifiable + material. The other cottonmouth contained one juvenile pond + turtle, _Pseudemys scripta_...." + + Texas: "... several ... feeding on frogs.... One ... found DOR + was found to contain a large catfish." (Guidry, 1953:54.) + +Of 246 cottonmouths that I examined for food items, only 46 contained +prey in their digestive tracts. Almost all of the snakes examined were +museum specimens that had been collected at many places over a period of +about 40 years. It was not known how long each had been kept alive +before being preserved. Therefore it was impossible to determine what +proportion of any population of cottonmouths could be expected to +contain food. The food items were not analyzed numerically because the +scales and hair, by means of which many food items in the intestine were +identified, yielded no clue as to the number of individuals actually +present unless several distinct kinds were found. Each occurrence of +scales or hair was thus recorded as a single individual, although some +such occurrences may have represented more than one animal. The contents +of some stomachs were so well digested that it was difficult to +determine the number of items present. As a rule only one food item was +present in a digestive tract, but a few tracts contained several items +of the same or different species. Three frogs (_Acris crepitans_) were +in one snake and three hylas (_Hyla versicolor_) in another. Still +another individual captured beside a drying pond contained six +individuals of _Lepomis_ each about three inches long and two pikes +(_Esox_) about six inches long. + + TABLE 13.--Analysis of Food Items of 46 Cottonmouths Collected + in Arkansas, Louisiana, and Texas (1922-1962). + + ===========================+========+==========+=========+========== + | | Number | Percent |Estimated|Estimated | + | | of | | | | + | |samples |frequency | weight |percentage| + | | in | | | | + | FOOD ITEMS | which | of | in | by | + | | item | | | | + | |occurred|occurrence| grams | bulk | + |---------------------------+--------+----------+---------+----------| + |Fish | (7) | 13.2 | 20 | 18.4 | + | _Esox_ sp. | 1 | | | | + | _Lepomis_ sp. | 2 | | 15 | | + | Unidentified | 4 | | | | + |Amphibians | (12) | 23.0 | | 20.4 | + | _Scaphiopus hurteri_ | 1 | | 13 | | + | _Acris crepitans_ | 2 | | 4 | | + | _Hyla cinerea_ | 2 | | 12 | | + | _Hyla versicolor_ | 1 | | 12 | | + | _Rana catesbeiana_ | 1 | | 20 | | + | _Rana pipiens_ | 3 | | 15 | | + | Unidentified | 2 | | | | + |Reptiles | (15) | 28.4 | | 29.9 | + | _Pseudemys scripta_ | 2 | | 15 | | + | _Anolis carolinensis_ | 1 | | 6 | | + | _Eumeces fasciatus_ | 1 | | 7 | | + | _Lygosoma laterale_ | 2 | | 5 | | + | _Natrix_ sp. | 1 | | 10 | | + | _Natrix erythrogaster_ | 2 | | 10 | | + | _Agkistrodon piscivorus_ | 2 | | 20 | | + | _Crotalus_ sp. | 1 | | 30 | | + | Unidentified snakes | 3 | | | | + |Birds | (4) | 7.6 | | 18.6 | + | _Anhinga anhinga_ (juv.) | 1 | | 60 | | + | Egret (head and neck) | 1 | | 20 | | + | Passeriformes | 2 | | 20 | | + |Mammals | (6) | 11.3 | | 12.7 | + | _Blarina brevicauda_ | 1 | | 12 | | + | Cricetinae | 5 | | 18 | | + |Unidentified | (9) | 17.0 | | | + ---------------------------+--------+----------+---------+----------- + +The "unidentified" category (Table 13) refers to jellylike masses in the +stomach or material in the intestine in which no scales, feathers, hair, +or bones could be found. Most of the unidentifiable matter could be +assumed to consist of remains of amphibians, since they leave no hard +parts. If this assumption is correct, amphibians comprise about 40 per +cent of the diet. Since intestinal contents were included, a volumetric +analysis was not feasible. Therefore, the weight of each type of food +item was estimated and the percentage by bulk calculated from it (Table +13). + +Pieces of dead leaves and small sticks constituted most of the plant +material found and presumably were ingested secondarily because they +adhered to the moist skin of the prey, especially to fish and +amphibians. However, some plant materials probably are eaten because +they have acquired the odor of the prey. One cottonmouth contained a +_Hyla cinerea_, several leaves, and five sticks from 37 to 95 +millimeters long and from 12 to 14 millimeters in diameter. + +Most reports in the literature state that gravid females do not feed, +but four gravid females examined by me containing large, well-developed +embryos also contained evidences of having recently fed. Two of them had +scales of snakes in the stomach or intestine, one contained a six-inch +_Lepomis_, and the other had hair in the intestine and the head and neck +of an adult egret in the stomach. + + + + +MORTALITY FACTORS + +Natural Enemies and Predators + + +Published records of other animals preying on cottonmouths or killing +them are few. Reptiles more often than other classes of vertebrates prey +on the cottonmouth. McIlhenny (1935:44) reported on the scarcity of +snakes in areas where alligators were present. Predation on cottonmouths +by indigo snakes (_Drymarchon corais_) was reported by Conant (1958:153) +and Lee (1964:32). Allen and Swindell (1948:6) obtained a photograph of +a king-snake (_Lampropeltis getulus_) killing a cottonmouth but thought +that moccasins are not eaten by _L. getulus_. However, one occasion +reported herein shows that cottonmouths are eaten by king-snakes; and +Clark (1949:252) reported finding 13 cottonmouths, along with other +prey, in the stomach contents of 301 king-snakes (_L. g. holbrooki_) +from northwestern Louisiana. Cannibalism is also common among +cottonmouths. Klauber (1956:1058;1079) cited predation on cottonmouths +by a blue heron (_Ardea herodias_) and a largemouth bass (_Micropterus +salmoides_). Man is probably the greatest enemy of the cottonmouth. +Intentional killing, capturing, road kills, and alteration of the +environment destroy large numbers. + + +Parasites and Diseases + +Allen and Swindell (1948:12) listed several diseases and parasites of +snakes and stated that "some moccasins captured in the woods are so poor +and weak from parasitic infection that they can barely crawl." The only +kind of ectoparasite found on captive cottonmouths in the course of my +study was a snake mite, _Ophionyssus natricus_. An infestation of that +mite was thought to be partly responsible for the death of one captive +moccasin. Other moccasins spent increasing amounts of time in their +water dish after they became infected with mites. Under natural +conditions frequent swimming probably keeps cottonmouths nearly free of +mites. + +Endoparasites found included lung flukes, stomach nematodes, and +tapeworms. Lung flukes (_Ochetosoma_ sp.) were found in 16 of 20 captive +cottonmouths. Snails and frogs serve as intermediate hosts for various +stages in the life cycle of these flukes. The high percentage of +cottonmouths infested with flukes is indicative of the use of frogs as a +major source of food. Less than ten flukes were usually observed in the +snakes' mouths but occasionally more were seen. One snake was observed +thrashing about in its cage for nearly an hour, after which time it +died. Upon examination of the mouth, 32 flukes were found, most of which +were located in the Jacobson's organs. Whether or not flukes caused the +death is not known. Nematodes (_Kalicephalus_ sp.) were found in the +stomach of each of several preserved specimens; most of these snakes had +no food in their digestive tracts. In a high percentage of the +moccasins, tapeworms (_Ophiotaenia_ sp.) were in the duodenum, in many +instances so tightly packed as seemingly to prevent passage of food. The +importance of fish in the diet is reflected by the high percentage of +snakes containing tapeworms. An unidentified cyst (?) about an inch long +and containing two hooks on one end was found attached to the outer wall +of the stomach of a cottonmouth. Yamaguti (1958) listed all the kinds of +helminths known from cottonmouths. + + +Miscellaneous Causes of Death + +Munro (1949:71-72) reported on the lethal effect of 10 per cent DDT +powder on two young cottonmouths which were dusted with it to kill +mites. Herald (1949:117) reported an equal effect caused by spraying a +five per cent DDT solution in a room with several snakes. All but three +large cottonmouths, which were under shelter at the time of spraying, +were killed. + +One individual that refused to eat was dissected soon after death, and a +short piece of a branch on which two large thorns were located at 90° +angles was found blocking the intestine at the posterior end of the +stomach. + +An unexpected and probably unusual circumstance caused the death of two +captives. After cleaning a cage containing five cottonmouths and placing +several mice in the cage for food, I noticed two of the snakes lying +stretched out, partially on one side, and almost unable to move. At +first I thought they had been bitten by other snakes which were in +pursuit of the mice. The two died after two days. When a similar +incident occurred in another cage, I removed the "bitten" snake and it +fully recovered after 11 days. When the same symptoms were observed in a +garter snake in another cage, I realized that in each instance the cage +had been cleaned and fresh cedar chips placed in it immediately prior to +observation of these symptoms. Fine cedar dust on the chips had +evidently poisoned the snakes. + + + + +BEHAVIOR + +Annual and Diel Cycles of Activity + + +In the days following emergence in spring, cottonmouths often endure +uncomfortable and even dangerous temperatures in order to obtain food +and mates. They are more sluggish at this time and more vulnerable to +predation than later in the season when temperatures are optimal. Fitch +(1956:463) found that copperheads in northeastern Kansas begin their +annual cycle of activity in the latter part of April, when the daily +maximum temperature is about 22° C. and the minimum is about 4° C., and +become dormant in late October or early November, at which time the +daily maximum temperature is about 15° and the minimum is about 0°. +Indications are that in the northern part of its range the annual +activity cycle of the cottonmouth resembles that of the copperhead in +northeastern Kansas. Klimstra (1959:2) captured cottonmouths from April +to October in southern Illinois. Barbour (1956:36) collected large +numbers of them in early April in Kentucky and stated that they migrate +from swamps to wooded hillsides in late August and early September. +Spring migrations begin after a few consecutive warm days in March. In +northern Oklahoma cottonmouths have been found along the Verdigris River +as early as March, suggesting that a few winter in crayfish holes and +mammal burrows. The majority of individuals found in this area were at +denning sites along cliffs above the river and emerged later than those +near the river (Dundee and Burger, 1948:1-2). In Virginia cottonmouths +have been seen as early as March 5 (Martin and Wood, 1955:237) and as +late as December 4. They have been observed in migration from the swamps +of the barrier beach to the mainland in late October and early November +in southeastern Virginia (Wood, 1954a:159). According to Neill +(1947:204), the cottonmouth tolerates lower temperatures than do most +snakes in Georgia and is one of the last to go into hibernation. Allen +and Swindell (1948:4) stated that cottonmouths usually bask during the +mornings of the cooler months in Florida, but they mentioned nothing of +denning such as occurs farther north. Although winter aggregations occur +in the northern parts of the range, I have never seen such aggregations +in the South. However, in one instance related to me by a reliable +observer, seven cottonmouths were found together on a creek bank near +the Gulf Coast in early spring. + +During late summer and early autumn, fat is deposited in lobes in the +lower abdomen in preparation for the period of winter quiescence. Gravid +females usually do not feed so frequently or so much as other snakes, +because they tend to become inactive as the ova develop. Whether or not +females feed heavily after parturition and previous to denning is not +known. Peaks of activity in autumn may be caused by final attempts to +feed before denning and by the appearance of large numbers of newborn +young. The young usually have from one to two months in which to feed +before the advent of cold weather. According to Barbour's (_op. +cit._:38) findings, the young probably feed before hibernation because +they grow substantially in winter. For those that do not feed, the rate +of survival is perhaps much lower. + +In preparation for winter, cottonmouths migrate inland, usually to dry +forested hillsides where they den, commonly among rocks at the tops of +bluffs, along with several other species of snakes. In such aggregations +there is no hostility and each individual may derive benefit from +contact with others by which favorable conditions of temperature and +humidity are maintained. + +Neill (1947:204) has found many specimens in winter by tearing bark from +rotting pine stumps on hillsides overlooking lakes or streams. On cold +days they evidently retreat below the surface, while on warm days they +lie just below the bark or emerge and bask. Neill believes that the use +of stumps by cottonmouths is an innate pattern of behavior, because of +the large number of young-of-the-year found in such surroundings. +Cottonmouths were observed in winter also under logs and stumps by Allen +(1932:17). I have twice observed cottonmouths crawling into crayfish +burrows along the Gulf Coast of Texas, and suppose they are used as +denning sites to some extent. + +The diel cycle of activity of cottonmouths is of necessity closely +related to the seasonal cycle. Since optimal temperatures determine +activity, the diel cycle varies greatly from time to time. It has been +well established that cottonmouths, like most other crotalids and many +snakes of other families, prefer nocturnal to diurnal activity, even +though the temperature may be less favorable at night. This preference +is correlated with increased nocturnal activity of frogs and reptiles +that constitute the principal food supply. + +During spring and autumn, activity is more restricted to the day and +long periods of basking occur. However, as hot weather approaches, +basking occurs mainly in the morning and evening and activity becomes +primarily nocturnal. But, in well shaded, moist forests, cottonmouths +feed actively in the daytime. + +Availability of food also has an important influence upon activity. +Allen and Swindell (_op. cit._:5) stated that moccasins congregate +around drying ponds and feed on dying fish until the moccasins can hold +no more. They then usually stay nearby as long as food remains. In an +area of the Stephen F. Austin Experimental Forest near Nacogdoches, +Texas, many cottonmouths journey daily to and from a swamp and a dry +field, evidently to feed on rodents inhabiting the area. Ten individuals +captured along a snake-proof fence that was built 30 yards from the +swamp were found lying coiled along the fence after 4:30 p.m., at which +time the area was shaded. On another occasion, I captured a large +cottonmouth that was feeding upon dying fish in a drying pool about +10:30 a.m. on August 19, 1962. + +Because of the aquatic habits of the cottonmouth, relative humidity +probably has little influence on the snake's activity. However, +cottonmouths are more restricted to the vicinity of water in dry weather +than during rains or muggy weather when many of their natural prey +species also move about more freely. Increased activity on cloudy days +may result from protection from long exposure to sunshine. Torrential +rains and floods, such as those following hurricanes along the Gulf and +Atlantic coasts of the southeastern United States, bring out quantities +of snakes of all species. Rattlesnakes and cottonmouths in particular +are killed by the thousands at these times because they seek shelter in +human habitations. However, these are unusual circumstances and do not +reflect voluntary activity as a result of preferences. + +Thermal reactions of reptiles were classified by Cowles and Bogert +(1944) into several categories. For each species there is a basking and +normal activity range limited by the voluntary minimum and voluntary +maximum at which the animal seeks shelter. Beyond this normal range are +the critical thermal minimum and critical thermal maximum (C. T. M.) at +which effective locomotion is prevented. The lethal minimum and maximum +are those temperatures at which short exposure produces irreparable +damage, and death inevitably results. These classifications are modified +somewhat by seasonal or laboratory acclimation or by the physiological +state of the animal. The C. T. M. of five cottonmouths was determined by +placing each individual in an enclosed area and heating it with an +infrared lamp. Cloacal temperatures were taken with a Schultheis +quick-recording thermometer as soon as the snake could no longer right +itself when placed on its back. All temperatures were in degrees +Celcius. The C. T. M. averaged 39.2° (38.0° to 40.0°). A temperature of +38.0° was lethal to one individual. These cottonmouths had been in +captivity for nine months. The behavior of the snakes during heating +resembled those instances described by Klauber (1956:382-387) for +rattlesnakes. As the body temperature of the snakes rose past the +optimum, each individual became disturbed and tried to escape from the +enclosure. The snakes soon became frantic in their efforts to escape. +After about five minutes the mouth was opened and heavy, slow breathing +was begun, accompanied by a loss of coordination and a slowing down of +movements. The snakes writhed spasmodically for a few seconds and then +lay still, usually with the mouth open. Recovery was begun by rolling on +the belly and flicking the tongue, followed by movements of the head and +then the body. Cottonmouths are rarely exposed to dangerously high +temperatures owing to their semi-aquatic habits, but there are probably +occasions when individuals reach the C. T. M. for the species. + + +Basking + +Since activity, digestion, and gestation depend upon adequate internal +temperatures, there must be a process by which these temperatures are +attained and for an appropriate time maintained. Basking is important in +this respect. The cottonmouths prefer to lie in a coiled position and, +during basking, can usually be found beside bodies of water or on +branches of dead trees overhanging the water. They are good climbers and +have a prehensile tail that is frequently employed in descending from +small branches. Since cottonmouths are semi-aquatic and are often +exposed to temperatures that are lower than those of the air, they +either must bask more often than terrestrial snakes or tolerate lower +temperatures. Length of the period of basking is determined not only by +amounts of insolation and temperature but also by the size of the snake. +A smaller snake can reach its optimum temperature more rapidly because +of a higher surface-to-volume ratio. Another factor that may play a +minor role in the rate of temperature change is the color of the snake. +The wide variation in color of cottonmouths probably affects rates of +heat increase and loss due to direct radiation. Slight hormonal control +of melanophores described in snakes by Neill and Allen (1955) also may +exert some influence on the length of time spent basking. No rates of +temperature increase or decrease are available for cottonmouths. + + +Coiling + +While inactive the cottonmouth spends most of its time lying in a coiled +position with the tail outermost, with the body usually wound into about +one and one-half cycles, and the head and neck in a reversed direction +forming a U- or S-shaped loop. From this position the snake is able to +make a short strike or a hasty getaway if necessary. In my opinion this +position is used primarily for basking or resting and only secondarily +for feeding. Most individuals appear to pursue their prey actively, not +lying in ambush for the approaching prey to the extent that most other +crotalids do. + +Many of the cottonmouths that I kept in captivity were observed in a +coiled position for periods up to three or four days. Under natural +conditions, however, they are more active. Young cottonmouths are +inclined to remain in a coiled position for longer periods than older +individuals. + + +Locomotion + +Four distinct types of locomotion have been described in snakes: +horizontal undulatory, rectilinear, sidewinding, and concertina +(Klauber, 1956: 331-350). Most snakes are capable of employing two or +more of these types of progression, at least to a certain degree; but +horizontal undulatory locomotion is the most common method used by the +majority of snakes, including the cottonmouth. In this method the +snake's body is thrown into lateral undulations that conform with +irregularities in the substrate. Pressure is exerted on the outside and +posterior surface of each curve, thus forcing the body forward. + +Rectilinear locomotion is more useful to large, thick-bodied snakes +which use this method of progression, chiefly when they are prowling and +unhurried. This method depends upon the movement of alternate sections +of the venter forward and drawing the body over the ventral scales +resting on the substratum by means of muscular action. This mode of +locomotion was most frequently observed in captive cottonmouths when +they were crawling along the edge of their cages, especially when they +were first introduced to the cages and toward the end of the shedding +process. The other two types of locomotion, sidewinding and concertina, +have not, to my knowledge, been observed in the cottonmouth. + +Both the cottonmouth and the cantil have definite affinities for water +and are as likely to be found in water as out of it. Copperheads and +rattlesnakes, although not aquatic, are good swimmers. When swimming, a +motion resembling horizontal undulatory progression is used. + + +Disposition + +The number of different opinions expressed in the literature concerning +the cottonmouth's disposition is not at all surprising. As with any +species there is a wide range of individual temperament, which is +affected by many factors. The cottonmouth is considered by some writers +to be docile while others consider it to be highly dangerous. Allen and +Swindell (1948:7) described the variability in temperament, even among +individuals. They wrote: "On rare occasions, moccasins are found which +will attack. A perfectly docile snake will turn and bite viciously +without any apparent reason." They also recounted a case in which a +cottonmouth was kept as a pet for six years, being allowed the freedom +of the house. Smith and List (1955:123) found them "... surprisingly +docile in the gulf region [Mississippi], displaying none of the +pugnacity of more northern cottonmouths." Smith (1956:310) stated: +"Unlike the copperhead, cottonmouths are pugnacious; their powerful +jaws, long fangs, vicious disposition and potent venom make them a very +dangerous animal." + +My own observations are in general agreement with the statements of +Allen and Swindell (_loc. cit._). In my encounters with cottonmouths, I +have never found any aggressive individuals except for three juveniles +that were born in captivity. In their first three days in the laboratory +these juveniles were observed to strike repeatedly whenever anyone +entered the room. After this short period of aggressiveness, however, +they slowly became more docile. The disposition shown by the newborn +young is clearly an innate behavioral pattern that undoubtedly has a +direct relationship to survival. The majority of cottonmouths that I +have approached in the field have moved swiftly to seek refuge in nearby +water; a few have remained motionless as I approached, and one showed +the typical threat display. Upon capture and handling, they react +similarly to other pit-vipers by opening and closing the mouth and +erecting the fangs in an attempt to bite. They often bite through the +lower jaw and eject venom at this time as well as when the mouth is +open. Of more than a dozen individuals kept in captivity, four were +particularly difficult to handle whereas another was extremely docile. +It was almost never found in aggregations with the other snakes and did +not struggle or attempt to bite when handled. The majority remained +unpredictable in disposition, usually appearing docile and lazy but +capable of extremely rapid movements when disturbed. + + +Defense and Escape + +The typical threatening posture of rattlesnakes is all but lacking in +the cottonmouth, which relies primarily on concealing coloration or +nearness to water for escape. When approached, it usually plunges into +nearby water or remains motionless with the head held up at a 45° angle +and the mouth opened widely exposing the white interior. The tail is +sometimes vibrated rapidly and musk is expelled. This threat display is +unique to cottonmouths; although it does not attract as much attention +as the display of rattlesnakes, it is probably an effective warning to +most intruders at close range. + +Neill (1947:205) reported one case in which a cottonmouth used the "body +blow" defense, described for _Crotalus_ by Cowles (1938:13), when +approached by a king-snake, _Lampropeltis getulus_. In this unusual +posture the anterior and posterior portions of the body are held against +the ground and the middle one-fourth to one-third of the body is lifted +up and used in striking the intruder. This same defense posture also was +observed in rattlesnakes when presented with the odor of the spotted +skunk, _Spilogale phenax_. However, the "king-snake defense posture" is +probably not a well-established behavioral pattern in the cottonmouth, +for it sometimes feeds upon king-snakes. I observed the killing and +devouring of a cottonmouth by a speckled king-snake, _L. g. holbrooki_; +the only attempts to escape were by rapid crawling and biting. + +Cottonmouths often squirt musk as a defensive action. The tail is +switched back and forth, and musk is emitted from glands on each side of +the base of the tail. The fine jets of musk are sprayed upward at about +45° angles for a distance of nearly five feet. How often this defense +mechanism is used against other animals is not known, but the musky odor +can frequently be detected in areas where cottonmouths are common. The +odor is repulsive and, if concentrated, can cause nausea in some +individuals. To me, the scent is indistinguishable from that of the +copperhead. + + +"Head Bobbing" + +"Head bobbing" in snakes has been described frequently in the +literature, and many interpretations have been advanced to explain its +occurrence. One of the earlier accounts was that of Corrington (1929:72) +describing behavior of the corn snake, _Elaphe guttata_. Characteristic +bobbing occurred when the snake was cornered, and seemingly the purpose +was to warn or frighten foes. Neill (1949:114-115) mentioned the jerking +or bobbing of the head in several species of snakes including the +cottonmouth, and remarked that "it is apparently connected with +courtship and with the recognition of individuals." According to Munro +(1950:88), "head bobbing" appears to be a sign of annoyance in some +instances but is usually concerned with reproduction and individual +recognition. Richmond (1952:38) thought that many types of head +movements among not only reptiles but also birds and some mammals are a +result of poor vision and serve "to delimit and orient an object that +for lack of motion is otherwise invisible." Head movements undoubtedly +occur in animals to facilitate accommodation, but it is obvious from +Richmond's conclusions that he has never observed "head bobbing" in +snakes. The term itself is grossly misleading and should be discarded. +Mansueti (1946:98) correctly described the movements as spastic +contractions of the body. I have observed numerous instances of these +movements in cottonmouths, copperheads, and rat snakes (_Elaphe +obsoleta_); and in no case has the movement resembled a head bob as is +described in lizards and other animals. The movement appears to be a +result of a nervous or sexually excited state and consists of highly +spastic contractions confined to the anterior part of the snake most of +the time but affecting the entire body on some occasions. + +I found the response to be most common among cottonmouths in confinement +when food was introduced to a cage containing several individuals +(increasing the tendency to strike at a moving object) and when an +individual was placed back in the cage after being handled. At these +times the snakes that were inactive began to jerk for a few seconds. +When the snake is in this seemingly nervous state, the same response is +elicited by another snake crawling over it. At other times the movement +of one individual causes no such response. The jerking movements appear +to be released by the recognition of a nervous state in another +individual and may serve to protect the jerking individual from +aggressive advances of the former. + +Where courtship is involved, the jerking motions are made in conjunction +with writhing of the male and do not result from the same type of +releaser described above. + + +Combat Dance + +The so-called combat dance between male snakes has long been known, but +its significance is still poorly understood. It was for many years +believed to be courtship behavior until the participants were examined +and found to be males. Carr and Carr (1942:1-6) described one such +instance in two cottonmouths as courtship. In their observations, as +well as those of others, copulation was never observed following the +"dance" but was assumed to be the ultimate goal. After the discovery +that only males participated, it was suggested that combat involved +competition for mates, but the "dance" has been observed at times other +than the breeding season (Ramsey, 1948:228). + +Shaw (1948:137-145) discussed the combat of crotalids in some detail but +drew no conclusions as to the cause of the behavior. Lowe (1948:134) +concluded with little actual evidence that combat among male snakes is +solely for territorial purposes. Shaw (1951:167) stated that combat may +occur as a possible defense against homosexuality. One case of +homosexual mating among cottonmouths was reported (Lederer, +1931:651-653), but the incomplete description seems to be of normal +courtship procedure except that the "female" tried to avoid the male. +Two instances of combat observed between timber rattlesnakes (_C. h. +horridus_) by Sutherland (1958:23-24) were definitely initiated because +of competition for food. More observations are needed before the +significance of the combat can be fully understood. + + + + +THE VENOM + +Properties of the Venom + + +The venom and poison apparatus have developed primarily as a means of +causing rapid death in small animals that are the usual prey. As a +protective device against larger enemies, including man, the venom may +have some value; but this was probably unimportant in the evolution of +the poison mechanism. A secondary function of the venom is to begin +digestion of tissues of the prey. Since food is swallowed whole, +injection of digestive enzymes into the body cavity enhances digestion +of the prey. + +Kellogg (1925:5) described venom as a somewhat viscid fluid of a +yellowish color and composed of 50 to 70 per cent proteins, the chief +remaining components being water and carbohydrates, with occasional +admixtures of abraded epithelial cells or saprophytic microorganisms. +Salts, such as chlorides, phosphates of calcium, magnesium, and +ammonium, occur in small quantities. Each of the components of snake +venom has a different effect on the body of the victim. It was at first +believed that there were two types of venoms: neurotoxic, which acts +upon nervous tissue; and haemotoxic, which acts on blood and other +tissues. It has since been found that venoms are composed of varying +mixtures of both types. Fairley (1929:301) described the constituents of +venom as: (1) neurotoxic elements that act on the bulbar and spinal +ganglion cells of the central nervous system; (2) hemorrhagins that +destroy the lining of the walls of blood vessels; (3) thrombose, +producing clots within blood vessels; (4) hemolysins, destroying red +blood corpuscles; (5) cytolysins that act on leucocytes and on cells of +other tissues; (6) elements that retard coagulation of the blood; (7) +antibactericidal substances; and (8) ferments that prepare food for +pancreatic digestion. Elapid snakes tend to have more of elements 1, 4, +and 6 in their venoms, while viperids and crotalids, of which the +cottonmouth is one, have higher quantities of elements 2, 3, and 5. +Kellogg (_loc. cit._) stated that venom of cottonmouths contains more +neurotoxin than that of rattlesnakes and not only breaks down the nuclei +of ganglion cells but also produces granular disintegration of the +myelin sheath and fragmentation of the conducting portions of nerve +fibers. + +Thus, venoms contain both toxic elements and non-toxic substances that +promote rapid spreading of the venom through the body of the victim. +Jacques (1956:291) attributed this rapid spreading to the hyaluronidase +content of venoms. + + +Venom Yield and Toxicity + +One of the most important yet undeterminable factors of the gravity of +snakebite is the amount of venom injected into the victim. Since this +volume varies considerably in every bite, attempts have been made to +determine the amount and toxicity of venom produced by each species of +poisonous snake. Individual yield is so variable that a large number of +snakes must be milked in order to determine the average yield. Even then +there remains an uncertainty as to how this amount may compare with that +injected by a biting snake. + +Wolff and Githens (1939b:234) made 16 venom extractions from a group of +cottonmouths in a two-year period. The average yield per snake +fluctuated between 80 and 237 milligrams (actual weight), and toxicity +measured as the minimum lethal dose for pigeons varied from 0.05 to 0.16 +milligrams (dry weight). No decrease in yield or toxicity was evident +during this period. Another group of cottonmouths from which venom was +extracted over a period of five years also showed no decrease in yield +or toxicity. Of 315 individual extractions the average amount obtained +from each individual was 0.55 cubic centimeters of liquid or 0.158 grams +of dried venom (28.0 per cent solids). The minimum lethal dosage (M. L. +D.) which was determined by injecting intravenously into 350-gram +pigeons was found to be 0.09 milligrams (dry weight). Each snake carried +approximately 1755 M. L. D.'s of venom. + +The record venom extraction for the cottonmouth was 4.0 cubic +centimeters (1.094 grams dried venom) taken from a five-foot snake which +had been in captivity for 11 weeks and milked five weeks earlier (Wolff +and Githens, 1939a:52). The average yield of venom of cottonmouths is +about three times the average yield reported for copperheads by Fitch +(1960:256), a difference correlated with the greater bulk and relatively +large head of the cottonmouth. + +Allen and Swindell (1948:13) stated that cottonmouth venom rates third +in potency, compared drop for drop to that of _Micrurus fulvius_ and +_Crotalus adamanteus_. Freshly dried cottonmouth venom tested on young +white rats showed the lethal dose to be from 23 to 29 milligrams per +kilogram of body weight. The venom of 11 one-week-old cottonmouths was +found to be more potent than that of adult males. Githens (1935:171) +rated _C. adamanteus_ venom as being weaker than that of the copperhead +(_A. contortrix_), which he rated only slightly lower than cottonmouth +venom. The crotalids which he ranked more toxic than cottonmouths are: +the Pacific rattlesnake (_C. viridis oreganus_) and the massasauga (_S. +catenatus_). He found _A. bilineatus_, _C. durissus_, and _C. v. +lutosus_ to have the same toxicity as cottonmouths. Minton (1953:214) +found that the intraperitoneal "lethal dose 50" (the dose capable of +killing half the experimental mice receiving injections of it) was 6.36 +milligrams per kilogram for copperheads. However, in later publications +Minton (1954:1079; 1956:146) reported that the "lethal dose 50" for +copperheads was 25.65 milligrams. Approximately the same potency was +determined for cottonmouths. Several rattlesnakes that he tested showed +a higher toxicity than copperheads or cottonmouths. + +Criley (1956:378) found the venom of copperheads to be 6.95, nearer +Minton's earlier estimate, and rated cottonmouth venom as being twice as +toxic as that of copperheads. The relative toxicities of other crotalids +tested, considering the cottonmouth to be one unit, were: _C. +basiliscus_, 0.3; _A. contortrix_, 0.5; _C. viridis oreganus_, 1.4; _A. +bilineatus_, 2.2; _C. adamanteus_, 2.3; _C. v. viridis_, 3.2; _C. +durissus terrificus_, 27.5. + +It can be seen from the above examples that toxicity of venoms and the +resistance of the animal receiving an injection of venom is highly +variable. Possibly the venom of each species of snake has greatest +effect on animals of the particular group relied on for food by the +snake. If that is so, the venom of cottonmouths would be expected to be +more toxic when tested on fish, reptiles, and amphibians than on birds +and mammals. Likewise, the venom of most species of rattlesnakes would +be expected to be more virulent when injected into mammals than when +injected into lower vertebrates. But, according to Netting (1929:108), +species of rattlesnakes that prey on cold-blooded animals, which are +less susceptible to venoms than warm-blooded animals, are thought to +have highly toxic venoms. This explanation accounts for the powerful +venom of _Sistrurus catenatus_; and, in this respect, venom of +cottonmouths should be highly toxic also. However, no clear-cut trends +have been shown in most cases. Allen (1937) injected 250-gram guinea +pigs with 4 milligrams of venom of various poisonous snakes. Survival +time was recorded in order to indicate the relative potency of the +venoms. Of 16 such tests _C. adamanteus_ held places 1, 2, 3, 12, and +16; _Bothrops atrox_ held places 4, 9, 10, and 13; and _A. piscivorus_ +held places 5, 7, 8, and 15. Places 6, 11, and 14 were held by three +individuals of different species. No relationship to size or sex was +indicated by the results of this experiment. + + +Susceptibility of Snakes + +Numerous experiments have been conducted to determine the susceptibility +of various snakes to venom. The majority of these experiments were +performed to learn whether or not venomous snakes were immune to their +own poison. Conant (1934:382) reported on a 30-inch cottonmouth that +killed two Pacific rattlesnakes and another cottonmouth. One rattlesnake +was bitten on the tail and the other on or near the head and partially +swallowed. Gloyd (1933:13-14) recorded fatal effects to a rattlesnake +from the bite of a cottonmouth. He also reported on the observations of +three other crotalids bitten by themselves or other snakes, from which +no harmful effects were observed. Allen (1937) injected several snakes +with dried cottonmouth venom which was diluted with distilled water just +before each injection. Four cottonmouths receiving 9, 18, 19, and 20 +milligrams of venom per ounce of body weight survived, while another +receiving 18.7 milligrams per ounce died after three hours. A specimen +of _S. miliarius_ receiving 8.3 milligrams per ounce died in about ten +hours, while a _C. durissus_ receiving 12.5 milligrams per ounce +succumbed in 45 minutes. An alligator receiving 6 milligrams per ounce +died in 14 hours. Even the snakes that survived showed some degree of +swelling. + +The studies of Keegan and Andrews (1942:252) show that king-snakes are +sometimes killed by poisonous snakes. A _Lampropeltis calligaster_ +injected with _A. contortrix_ venom (0.767 milligrams per gram) died +five days following the injection. This amount was more than twice the +amount of _A. piscivorus_ venom injected into a _L. getulus_ by Allen +(1937) in which the snake showed no ill effects. Keegan and Andrews +(_loc. cit._) stated that success in overpowering and eating poisonous +snakes by _Lampropeltis_ and _Drymarchon_ may be due to the ability to +avoid bites rather than to immunity to the venom. However, Rosenfeld and +Glass (1940) demonstrated that the plasma of _L. g. getulus_ had an +inhibiting effect on the hemorrhagic action on mice of the venoms of +several vipers. + +One of the more extensive studies on effects of venoms on snakes is that +by Swanson (1946:242-249). In his studies freshly extracted liquid venom +was used. His studies indicated that snakes are not immune to venom of +their own kind or to closely related species. Copperhead venom killed +copperheads faster than did other venoms but took more time to kill +massasaugas, cottonmouths, and timber rattlers. However, most of the +snakes were able to survive normal or average doses of venom although +they are not necessarily immune to it. + +One of the major problems in comparing the data on toxicity of venom in +studies of this type is that no standard method of estimating toxicity +has been used. Swanson's (_loc. cit._) amount of venom equalling one +minim (M.L.D.?) ranged from 0.058 to 0.065 cubic centimeters. There were +no different values given for each species, but the time that elapsed +from injection of the venom to death represented the toxicity. There +also was no attempt in his study to convert the amount of venom used +into a ratio of the volume of venom per weight of snake, making the +results somewhat difficult to interpret. Additional work in this field +should provide for many injections into many individuals of several size +classes. The studies to date have been on far too few individuals to +allow statistical analyses to be accurate. + + + + +THE BITE + +Effects of the Bite + + +Factors determining the outcome of snakebite are: size, health, and +species of snake; individual variation of venom toxicity of the species; +age and size of the victim; allergic or immune responses; location of +the bite; and the amount of venom injected and the depth to which it is +injected. The last factor is one of the most variable, owing to (1) +character and thickness of clothing between the snake and the victim's +skin, (2) accuracy of the snake's strike, and (3) size of the snake, +since a large snake can deliver more venom and at a greater depth than +can a small snake. + +Pope and Perkins (1944) demonstrated that pit-vipers of the United +States bite as effectively as most innocuous snakes and that a careful +study of the bite may reveal the location of the pocket of venom, size +of the snake, and possibly its generic identity (see Dentition). The +bite pattern of the cottonmouth as well as the other crotalids showed +the typical fang punctures plus punctures of teeth on both the pterygoid +and mandible. Even so, a varying picture may be presented because from +one to four fang marks may be present. At times in the fang-shedding +cycle three and even four fangs can be in operation simultaneously. + +Various authors have attributed death of the prey to the following +causes: paralysis of the central nervous system, paralysis of the +respiratory center, asphyxiation from clotting of the blood, stoppage of +the heart, urine suppression due to crystallized hemoglobin in the +kidney tubules, dehydration of the body following edema in the area of +the bite, or tissue damage. Mouths of snakes are reservoirs for +infectious bacteria, which are especially prolific in damaged tissue. +Bacterial growth is aided by the venom which blocks the bactericidal +power of the blood. + +Three grades in the severity of snakebite (I, minimal; II, moderate; and +III, severe) were described by Wood, Hoback, and Green (1955). Parrish +(1959:396) added a zero classification to describe the bite of a +poisonous snake in which no envenomation occurred. Grade IV (very +severe) was added by McCollough and Gennaro (1963:961) to account for +many bites of the eastern and western diamondback rattlesnakes. + +The first symptom of poisonous snakebite is an immediate burning +sensation at the site of the bite. Within a few minutes the loss of +blood into the tissues causes discoloration. Swelling proceeds rapidly +and can become so great as to rupture the skin. Pain is soon felt in the +lymph ducts and glands. Weakness, nausea, and vomiting may ensue at a +relatively early stage. Loss of blood into tissues may spread to the +internal organs. In conjunction with a rapid pulse, the blood pressure +and body temperature can drop. Some difficulty in breathing can occur, +especially if large amounts of neurotoxin are present in the venom. In +severe cases the tension due to edema obstructs venous and even arterial +flow, in which case bacteria may multiply rapidly in the necrotic tissue +and gangrene can occur. Blindness due to retinal hemorrhages may occur. +Symptoms of shock may be present after any bite. + + +Treatment + +Perhaps one of the most important factors in the outcome of snakebite is +the treatment. Because of the variable reactions to snakebite, treatment +should vary accordingly. Many methods have been proposed for treating +snakebite, and there is disagreement as to which is the best. The list +of remedies that have been used in cases of snakebite includes many that +add additional injury or that possibly increase the action of the venom. +The use of poultices made by splitting open living chickens and the use +of alcohol, potassium permanganate, strychnine, caffeine, or injection +of ammonia have no known therapeutic value, and may cause serious +complications. The most important steps in the treatment of snakebite +are to prevent the spread of lethal doses of venom, to remove as much +venom as possible, and to neutralize the venom as quickly as possible. + +It is generally agreed that the first step in snakebite treatment should +be to place a ligature above the bite to restrict the flow of venom, and +also to immobilize the patient as much as possible. The ligature should +be loosened at least every fifteen minutes. The next steps are +sterilization of the skin and the making of an incision through the fang +punctures. As pointed out by Stahnke (1954:8), the incision should be +made in line with the snake's body at the time of the bite, so as to +account for the rearward curvature of the fangs and possibly to reach +the deposition of venom. Many instruction booklets and first-aid guides +have specified the length and depth of incision to be made, but the +actual size and depth of the cut should depend upon the location of the +bite. An "X" cut or connection of the fang punctures is likely to +facilitate the spread of the venom. No cut should be made that would +sever a large blood vessel or ligament. + +Extensive damage is often caused by well-meaning individuals whose +attempts at first aid result in brutally deep incisions and tourniquets +applied too tightly and for too long a period of time; the resultant +damage in many instances exceeds that of the bite itself (Stimson and +Engelhardt, 1960:165). Stimson and Engelhardt also think that time +should be sacrificed to surgical cleanliness, and incisions should not +be made if a hospital can be reached within an hour. + +The ligature-cryotherapy (L-C) method proposed by Stahnke (1953) has +been severely criticized by other workers. He stated that the ligature +should be tight enough to restrict completely the flow of venom until +the temperature of the area can be lowered sufficiently to prevent any +action of the venom. After 10 minutes the ligature may be removed and +the bitten area kept immersed in a vessel of crushed ice and water. If +the envenomized member is to be treated for more than four hours (which +is the case with almost all pit-viper bites), it should be protected by +placing it in a plastic bag. The venom action should be tested after 12 +or more hours. This consists of a brief warming period to determine +whether or not the action of the venom can be felt. The patient should +be kept warm at all times; and the warming at the termination of +treatment should be done gradually, preferably by allowing the water to +warm slowly to room temperature. + +Advocates of the L-C method warn against making incisions unless they +are absolutely necessary, the theory being that each cut permits +additional bacterial infection and does little good in removing venom. +However, McCollough and Gennaro (1963:963) demonstrated that, in bites +where the fangs had only slightly penetrated the skin, more than 50 per +cent of the venom was removed in some instances if suction was started +within three minutes after the injection. With deeper injection the +amount of venom recovered sometimes reached 20 per cent of the dose. +Stahnke suggested that an incision be made at the site of the bite only +after the site has been refrigerated for at least 30 minutes. + +Stimson and Engelhardt (_loc. cit._) stated that two constricting bands +should be used between the bite and the body and that cracked ice in a +cloth should be applied to the bite before reaching a hospital. In +addition, they suggested the following procedure. Rings of incisions +should follow the swelling, and suction should continue for several +hours. After the edema has receded, the limb should be wrapped in a +towel containing crushed ice. Antivenin should be given only in severe +cases. Calcium gluconate and gas gangrene antitoxin as well as +antibiotics are helpful. + +The most recent and up-to-date summary of snakebite treatment is that by +McCollough and Gennaro (1963). Following is a brief summary of their +suggestions: + + 1. Immobilization--Systemic immobilization is effected by body + rest and locally by splinting the bitten area. + + 2. Tourniquet--A lightly occlusive tourniquet during a 30- to + 60-minute period of incision and suction would seem to possess + some advantages. In severe cases where medical attention is + hours away, a completely occlusive tourniquet may be necessary + to prevent death. Sacrifice of the extremity may be necessary + for the preservation of life. + + 3. Incision and suction--Suction should begin three to five + minutes after injection of venom if symptoms of poisoning are + present. Incisions one-fourth inch to an inch long across each + fang mark should be made in order to open the wound for more + efficient suction. Multiple incisions are not useful for the + removal of venom but may be employed under hospital conditions + to reduce subcutaneous tensions and ischemia. + + 4. Cryotherapy--An ice cap over the site of the bite for relief + of pain would seem to be permissible, especially prior to the + administration of antivenin. It must be remembered that cooling + during the administration of the antivenin radically reduces + the access of the antiserum to the bite area. + + 5. Antivenin--Antiserum is the keystone to the therapy of + snakebite. Careful evaluation of the severity of the bite and + the patient's sensitivity should be made before the use of + antivenin. In Grade II (moderate) bites, the intramuscular + injection on the side of the bite may suffice. In Grades III + (severe) and IV (very severe), shock and systemic effects + require intravenous injection. In bites producing symptoms of + this severity, antivenin must be given in amounts large enough + to produce clinical improvement. Ten to 20 units may be + necessary to prevent the relapse that sometimes occurs after + small doses of antivenin. Permanent remission of swelling and + interruption of necrosis are the therapeutic end point in the + clinical use of the antiserum. + +In all cases of snakebite where there is any doubt as to the snake's +identity, it should be killed if possible and taken to the hospital for +positive identification. In many instances of actual bites by poisonous +snakes the only treatment needed was an injection of tetanus antitoxin +or toxoid and sedation, because physical examination revealed no +indication of poisoning (Stimson and Engelhardt, _loc. cit._). + + +Case History of a Bite + +On July 29, 1963, at 8:20 a.m., I was treating a nine-month-old +cottonmouth for mites. As I dropped the snake into a sink, it twisted +its head and bit the tip of my right middle finger with one fang. The +fang entered just under the fingernail and was directed downward, the +venom being injected about five millimeters below the site of fang +penetration. After placing the snake back in its cage, I squeezed the +finger once to promote bleeding, wrapped a string around the base of the +finger, and drove to Watkins Memorial Hospital on the University of +Kansas campus. I began to feel a burning sensation in the tip of the +finger almost immediately. Upon my arrival at the hospital, an +additional ligature was placed around my wrist. At 8:30 a.m. a small +incision was made in the end of the finger, which by this time was +beginning to darken at the point of venom deposition. I sucked on the +finger until 8:35 a.m., when a pan of ice water that I had requested was +brought to me. No pain was felt except that caused by the ice. Fresh ice +was added as needed to keep the temperature low. By 9:30 a.m. the +finger had swollen and stiffened. At 10:00 a.m. the swelling had +progressed to the index finger and back of the hand. I experienced +difficulty in opening and closing the hand. Blood oozed slowly from the +incision. A dull ache persisted and about every two to four minutes a +sharp throb could be felt until nearly 11:00 a.m., when the pain +diminished. The rate and intensity of throbbing increased whenever the +hand was removed from the ice bath for more than a few seconds. Although +only the hand was immersed, the entire forearm was cold. Pain was felt +along the lymphatics on top of the arm when it was touched, and by 1:00 +p.m. a slight pain could be felt in the armpit. Since swelling and pain +were almost nonexistent by 2:00 p.m., I was permitted to leave. After +walking to a nearby building, I again felt a burning sensation as the +hand warmed. I made another ice bath and again immersed the hand in it +until 4:10 p.m., at which time it was removed from the water. The pain +and swelling began anew, and the hand was placed back in an ice bath +from 5:30 p.m. until about 7:30 p.m. At this time cryotherapy was +discontinued. From 10:00 p.m. to 12:00 midnight my legs twitched +periodically, and pain could be felt in both armpits. A slight +difficulty in breathing also was experienced for a short time. The acute +pain and burning sensation remained in the finger until the following +morning, but swelling progressed only as far as the wrist. The only +discomfort that day was in the finger. The tip was darkened, the entire +first digit red and feverish, and the lymphatics still painful when +touched. By the third day the swelling had regressed. The incision +itself was the main cause of discomfort, and the soreness at the site of +the bite persisted for at least four days. + +Although the L-C method of snakebite treatment has been vigorously +attacked by many, there is still need of much more data before it +can be unequivocally condemned or praised. It was preferred in the +treatment of this bite because: I knew that envenomation was minimal +and that there would be no need for antivenin; only one fang of a +snake less than one foot long had entered the tip of the finger; the +snake had bitten three frogs in the previous two days and had +possibly used up a considerable amount of its venom; the venom was +deposited at such a shallow depth that at least a portion of it +could be removed by suction; and the wound bled freely even before +suction was applied. The ice water was uncomfortably cold but was +not cold enough to cause frostbite, a major objection to the L-C +method. Ideally, fresh ice should be added little by little to +replace that which is melting, and the immersed area should be +protected from the water by a plastic bag. Pain and swelling can be +minimized by cryotherapy, but I would recommend its use only in +cases of mild poisoning such as the one described herein. + + +Snakebite in the United States + +Many estimates have been made of the number of bites of poisonous snakes +that occur annually in the United States. The occurrence of poisonous +snakebite has been nearly as badly underestimated as fatal results of +their envenomations have been overrated. For important data on number of +persons bitten by poisonous snakes in the United States, see the +following: Allen and Swindell (1948:15); Githens (1935:172); Klauber +(1956:811); Parrish (1963); Sowder and Gehres (1963:973); Stimson and +Engelhardt (1960:153); Swaroop and Grab (1956:441); Swartzwelder +(1950:579); Willson (1908:530); and Wood (1954b:937). + +Judging from estimates made in several states, the number of poisonous +snakebites in the United States would be about 5000 per year. In the +region where the cottonmouth occurs there are approximately 2000 persons +bitten annually by poisonous snakes. Of these approximately 39 per cent +are copperhead bites, 30 per cent each are cottonmouth and rattlesnake +bites, and I per cent are coral snake bites. These percentages vary +considerably from place to place, because of the distribution and +abundance of the eight species of poisonous snakes whose ranges overlap +that of the cottonmouth. + +According to Parrish (1963), about 14 people die of snakebite each year +in the United States. Of these deaths, about 6.6 per cent are +attributable to cottonmouths, 77.0 per cent to rattlesnakes, and 1.6 per +cent to coral snakes; 14.8 per cent are unidentified. Almost half of the +fatalities are in persons less than 20 years of age, the high mortality +rate being partially due to the greater ratio of venom to body weight. + + + + +SUMMARY + + +In my study, 306 living and preserved cottonmouths were examined. This +species occurs throughout the coastal plains of the southeastern United +States, usually at altitudes of less than 500 feet but occasionally up +to altitudes of more than 2000 feet. + +Two subspecies are recognized: the eastern cottonmouth, _A. p. +piscivorus_, occurring from extreme eastern Mississippi to southeastern +Virginia and Florida; and the western cottonmouth, _A. p. leucostoma_, +occurring from eastern Mississippi northward to southern Illinois and +Missouri and westward to central Texas. Intergradation occurs in eastern +Mississippi. + +The northern edge of the range is probably limited by low temperatures +in winter, and the western edge by lack of available habitat resulting +from insufficient precipitation. Old records of occurrence indicate that +the range has decreased in the last 100 years. The species inhabits +mostly areas where water is found, but at times wanders a mile or more +from the nearest water. + +The ground color is predominantly a brown, but varies from a +brownish-green to almost black with a pattern of 10 to 17 irregular +bands of a darker shade of brown. The pattern is better defined in the +eastern subspecies than in the western. + +The scutellation resembles that of other species of _Agkistrodon_. In +the specimens examined supralabials ranged from 7 to 9, and infralabials +from 8 to 12. The number of dorsal scale rows on the neck, at mid-body, +and immediately anterior to the anus is relatively constant at 27-25-21, +respectively. Ventral scales of 34 males averaged 134.4 (128 to 139), +and those of 48 females 133.5 (128 to 137). The number of caudal scales +showed some degree of sexual dimorphism; the average was 45.4 (41 to 50) +in 34 males and 42.6 (39 to 49) in 44 females. In general, caudal scales +on the basal half of the tail are undivided, whereas those on the distal +half are divided. No marked geographical variation was found in any +scale character. + +The poison fangs vary in length from 1.3 per cent of snout-vent length +in juveniles to 1.0 per cent in large adults. Fangs of captive +cottonmouths were shed and replaced at intervals of about 21 days, but +the interval was variable. Relationships in distance between the base of +fangs and between fang punctures in an actual bite indicate that +examination of the wound does not provide a good basis for judging +accurately the size of the snake that inflicted the bite. + +In general, females less than 450 millimeters in snout-vent length were +juveniles; those more than 450 millimeters were classified as post +partum or reproductive on the basis of sizes of ovarian follicles. Since +about half the adult females were fecund, it was concluded that a +biennial reproductive cycle occurs in this species. An annual cycle may +occur in areas where temperature permits year-round activity. It was +estimated that females become sexually mature at an age of approximately +two and one-half years. Mating is probably most concentrated in early +spring at about the time when females ovulate, but copulation is not a +stimulus for ovulation. Sperm retention and delayed fertilization allow +young to be produced without copulation occurring in each breeding +season. The testes increase in size gradually rather than rapidly at +maturity or in each breeding season, but seasonal cycles in sperm +production occur. + +The gestation period is three and one-half to four months. Determination +of sex in the embryos is possible by late June, because the hemipenes of +males are evaginated until the time of birth. Parturition generally +occurs in August or September, but captivity may delay birth for a month +or more. From one to 16 young per litter are born, depending on size of +the mother and other factors; but the average is between six and seven. +Mortality rate at birth is high in captive individuals but has not been +determined in natural populations. The sex ratio in embryos and adults +examined revealed about 53 per cent females. Because sufficient +information on population composition is not available, an estimate of +the percentage of adults in a natural population was based upon the +number found in my study. The reproductive potential was estimated from +these figures. + +Normal young at birth are 230 to 240 millimeters in snout-vent length, +but their size is influenced by the condition of the mother. Comparison +of newborn young with those captured in spring indicates that little +growth occurs during winter. Early growth is largely dependent upon +feeding before winter quiescence. + +The umbilical cord is broken at birth and the navel closes within a few +days, but the scar remains throughout life. Sexual dimorphism in the +position of the scar is characteristic of some snakes but is minimal in +cottonmouths. + +In those snakes more than 700 millimeters in length, males outnumber +females three to one. The maximum age of cottonmouths in nature is +unknown, but one has been kept in captivity for more than 18 years. + +Allometric growth is striking in cottonmouths. The head and tail are +proportionately longer in young individuals than in adults; and in males +the tail is, on the average, slightly longer than in females of the same +size. + +Shedding of the skin provides for growth and wear in snakes. The young +shed within a few days after birth and generally shed more frequently +than adults. Frequency of shedding depends mostly on amount of food +consumed, and there is some evidence that injuries on the head and neck +increase the frequency of shedding. Before shedding, the eyes become +cloudy for about five and one-half days, then clear up again for about +four days before the skin is shed. + +The food of cottonmouths consists mainly of small vertebrates and +occasionally invertebrates that are found near water. Fish, amphibians, +and reptiles make up nearly 70 per cent of the diet. Carrion is also +eaten and cannibalism occurs occasionally. Food is obtained by lying in +ambush or by active searching. The young are known to lure their prey +within striking range by waving their yellow tails in a manner +suggestive of writhing grubs. The method of obtaining prey differs +according to the kind of prey. Generally, cottonmouths retain their hold +on fish or frogs but release mice and larger prey after delivering a +bite. + +The major causes of mortality of cottonmouths are obscure. Predators are +known to include alligators, indigo snakes, king-snakes, largemouth +bass, and blue herons; there are probably numerous others. Heavy +parasitic infestations were found among the snakes examined. Snake +mites, _Ophionyssus natricus_, became increasingly abundant on almost +all captive snakes in April and May of 1963. Lung flukes (_Ochetosoma_ +sp.) were in 16 of 20 captive snakes, and many preserved specimens +contained nematodes (_Kalicephalus_ sp.) in the stomach and/or tapeworms +(_Ophiotaenia_ sp.) in the intestine. Although parasitic infestation +causes discomfort and may lower resistance to other detrimental factors, +it is difficult to attribute death to the effect of any particular kind +of parasite. Miscellaneous causes of death of some captive snakes also +were discussed. + +The maximal body temperatures tolerated by four cottonmouths were +between 38° and 40° C., but a temperature of 38° was lethal to a fifth +individual. Cottonmouths have been found on occasion when other snakes +were inactive because of low temperatures, but minimal temperatures +tolerated by this species are not known. The annual cycle of activity is +dependent upon temperature and thus varies from north to south. +Cottonmouths generally migrate inland in autumn, usually to dry forested +hillsides, where they den along with other species of snakes. After a +few warm days in spring they migrate back to the water's edge. The diel +activity cycle likewise depends upon temperatures but is influenced by +other factors as well. In spring and autumn, the snakes are active +mostly on warm, sunny days, whereas in summer they are active mostly at +night. In order to maintain adequate internal temperatures, much time is +spent basking mostly in a characteristic flat, resting coil either +beside a body of water or above water on limbs of dead trees. In this +position the snake is ready either for a short strike or a hasty +getaway. + +Juveniles appear particularly aggressive and strike repeatedly when +approached, a behavioral pattern definitely favoring survival. Adults +vary in disposition, usually appearing sluggish and lazy, but they are +capable of striking rapidly when disturbed. The typical threat display +consists of lying in a coiled position with the mouth opened widely, +exposing the white interior, and with the tail vibrating rapidly. The +striking posture resembles the resting coil except that the anterior +part of the body is raised off the ground and the mouth is sometimes +opened. Musk is often ejected in a fine spray from glands in the tail as +a further defensive action. + +"Head bobbing," more properly described as spastic contractions of the +body, was observed in captives when food was introduced into a cage +containing several individuals or when one of the snakes was returned to +the cage after being handled. Reports in the literature also have +connected these jerking movements with courtship. The response appears +to be elicited whenever a nervous state is recognized in another +individual and may serve to protect the jerking individual from +aggressive advances of the former. + +The relatively heavy appearance of the body, sluggish habits, and +cryptic coloration are correlated with the development of venom and +fangs. The poison apparatus has developed primarily as a means of +causing rapid death in prey and secondarily, perhaps, to begin the +digestion of small animals that are the usual prey, but it is also +important as a defensive device. The venom contains at least eight +constituents that aid in its action on prey. Toxicity of the venom is +difficult to determine because of numerous variables, but cottonmouth +venom is generally believed to be less potent than that of most +rattlesnakes and more potent than that of the copperhead. Snakes in +general are more resistant to snake venoms than other vertebrates of +similar size, but there is no immunity even to their own venom. + +About ten per cent of the approximately 5000 bites of poisonous snakes +per year in the United States are attributable to cottonmouths, and +about seven per cent of the approximately 14 deaths per year are caused +by cottonmouths. + + + + +LITERATURE CITED + + +ALLEN, E. R. + + 1937. Florida snake venom experiments. Florida Acad. Sci., 2:7 pp. + +ALLEN, E. R., and SWINDELL, D. + + 1948. Cottonmouth moccasin of Florida. Herpetologica, 4:1-16 (first + supplement). + +ALLEN, M. J. + + 1932. 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The umbilical scar, a sexually dimorphic character in + _Heterodon platyrhinos_. Nat. Hist. Misc., 83:1-2. + +FAIRLEY, N. H. + + 1929. The present position of snake bite and the snake bitten in + Australia. Med. Jour. Australia, 1(10):296-313. + +FITCH, H. S. + + 1956. Temperature responses in free-living amphibians and reptiles + in northeastern Kansas. Univ. Kansas Publ. Mus. Nat. Hist., + 8(7):417-476, 10 figs., 6 tables. + + 1960. Autecology of the copperhead. Univ. Kansas Publ. Mus. Nat. + Hist., 13(4):85-288, pls. 13-20, 26 figs. + +FORCE, E. R. + + 1930. The amphibians and reptiles of Tulsa County, Oklahoma, and + vicinity. Copeia, 1930(2):25-39. + +FOX, W. + + 1948. Effect of temperature on development of scutulation in the + garter snake, _Thamnophis elegans atratus_. Copeia, + 1948(4):252-262. + +GITHENS, T. S. + + 1935. Studies on the venoms of North American pit vipers. Jour. + Immun., 29(2):165-173. + +GLISSMEYER, H. R. + + 1951. Symposium. A snake den in Tooele County, Utah. Egg production + of the great basin rattlesnake. Herpetologica, 7(1):24-27. + +GLOYD, H. K. + + 1933. On the effects of moccasin venom upon a rattlesnake. Science, + 78(2010):13-14. + + 1934. Studies on the breeding habits and young of the copperhead, + _Agkistrodon mokasen_ Beauvois. Papers Michigan Acad. Sci., Arts + and Letters, 19:587-604. + +GLOYD, H. K., and CONANT, R. + + 1943. A synopsis of the American forms of _Agkistrodon_ + (copperheads and moccasins). Bull. Chicago Acad. Sci., + 7(2):147-170, 16 figs. + +GOODMAN, J. D. + + 1958. Material ingested by the cottonmouth, _Agkistrodon + piscivorus_, at Reelfoot Lake, Tennessee. Copeia, 1958(2):149. + +GUIDRY, E. V. + + 1953. Herpetological notes from southeastern Texas. Herpetologica, + 9:49-56. + +HALL, H. H., and SMITH, H. M. + + 1947. Selected records of reptiles and amphibians from southeastern + Kansas. Trans. Kansas Acad. Sci., 49(4):447-454. + +HAMILTON, W. J., JR., and POLLACK, J. A. + + 1955. The food of some crotalid snakes from Fort Benning, Georgia. + Nat. Hist. Misc., 140:1-4. + +HERALD, E. S. + + 1949. Effects of DDT oil solution upon amphibians and reptiles. + Herpetologica, 5(6):117-120. + +HICKMAN, C. P. + + 1922. A northern record for the water moccasin. Copeia, + 1922(106):39. + +HURTER, J. H. + + 1897. A contribution to the herpetology of Missouri. Trans. Acad. + Sci. St. Louis, 7:499-503. + +JACQUES, R. + + 1956. The hyaluronidase content of animal venoms. Pp. 291-293 _in_ + Venoms (ed. Buckley, E. E., and Porges, N., Amer. Assoc. Adv. Sci., + Publ. No. 44). + +KEEGAN, H. L., and ANDREWS, T. F. + + 1942. Effects of crotalid venom on North American snakes. Copeia, + 1942:251-254. + +KELLOGG, R. + + 1925. Poisonous snakes of the United States. U. S. D. A. Papers + (371), 13 pp. + +KLAUBER, L. M. + + 1941. Four papers on the application of statistical methods to + herpetological problems. Bull. Zool. Soc. San Diego, 17:1-95. + + 1956. Rattlesnakes. Univ. California Press, 2 vols., xxix + 1476 + pp. + +KLIMSTRA, W. D. + + 1959. Food habits of the cottonmouth in southern Illinois. Chicago + Acad. Sci., Nat. Hist. Misc., 168:1-8. + +LAUGHLIN, H. E. + + 1959. Stomach contents of some aquatic snakes from Lake McAlester, + Pittsburgh County, Oklahoma. Texas Jour. Sci., 11(1):83-85. + +LEDERER, G. + + 1931. Aus meinem Tagebuch. Wachenschrift fur Aquar. und Terr'kde., + 28:651-653. + +LEE, H. T. + + 1964. Letters to the Editor, Texas Game and Fish Mag., 22(3):32. + +LOWE, C. H., JR. + + 1948. Territorial behavior in snakes and the so-called courtship + dance. Herpetologica, 4(4):129-145. + +MANSUETI, R. + + 1946. Mating of the pilot blacksnake. Herpetologica, 3:98-100, 1 + fig. + +MARTIN, J. R., and WOOD, J. T. + + 1955. Notes on the poisonous snakes of the Dismal Swamp area. + Herpetologica, 11(3):237-238. + +MCCOLLOUGH, N. C., and GENNARO, J. F., JR. + + 1963. Evaluation of venomous snake bite in the southern United + States from parallel clinical and laboratory investigations. Jour. + Florida Med. Assn., 49(12):959-967. + +MCILHENNY, E. A. + + 1935. The alligator's life history. The Christopher Publ. House, + Boston, Massachusetts, 117 pp. + +MINTON, S. A., JR. + + 1953. Variation in venom samples from copperheads (_Agkistrodon + contortrix mokeson_) and timber rattlesnakes (_Crotalus horridus + horridus_). Copeia, 1953:212-215. + + 1954. Polyvalent antivenin in the treatment of experimental snake + venom poisoning. Amer. Jour. Trop. Med. and Hyg., 3:1077-1082. + + 1956. Some properties of North American pit viper venoms and their + correlation with phylogeny. Pp. 145-151 _in_ Venoms (ed. Buckley, + E. E., and Porges, N., Amer. Assoc. Adv. Sci., Publ. No. 44). + +MUNRO, D. F. + + 1949. Effect of DDT powder on small cottonmouths. Herpetologica, + 5:71-72. + + 1950. Additional observations on head bobbing by snakes. + Herpetologica, 6:88. + +NEILL, W. T. + + 1947. Size and habits of the cottonmouth moccasin. Herpetologica, + 3:203-205. + + 1949. Head bobbing, a widespread habit of snakes. Herpetologica, + 5:114-115. + + 1960. The caudal lure of various juvenile snakes. Quart. Jour. + Florida Acad. Sci., 23(3):173-200, 2 figs. + +NEILL, W. T., and ALLEN, E. R. + + 1955. Metachrosis in snakes. Quart. Jour. Florida Acad. Sci., + 18(3):207-215. + +NETTING, M. G. + + 1929. The venom of _Sistrurus catenatus_. Bull. Antivenin Inst. + Amer., 2(4):108-109. + +PARRISH, H. M. + + 1959. Poisonous snakebites resulting in lack of venom poisoning. + Virginia Med. Month, 86:396-401. + + 1963. Analysis of 460 fatalities from venomous animals in the + United States. Amer. Jour. Med. Sci., 245(2):35-47. + +PARRISH, H. M., and POLLARD, C. B. + + 1959. Effects of repeated poisonous snakebite in man. Amer. Jour. + Med. Sci., 237(3):277-286. + +PENN, G. H. + + 1943. Herpetological notes from Cameron Parish, Louisiana. Copeia, + 1943(1):58-59. + +PERKINS, C. B. + + 1955. Longevity of snakes in captivity in the United States. + Copeia, 1955(3):262. + +POPE, C. H., and PERKINS, R. M. + + 1944. Differences in the patterns of bites of venomous and of + harmless snakes. Archives of Surgery, 49:331-336. + +RAHN, H. + + 1942. The reproductive cycle of the prairie rattler. Copeia, + 1942(4):233-240. + +RAMSEY, L. W. + + 1948. Combat dance and range extension of _Agkistrodon + piscivorus leucostoma_. Herpetologica, 4:228. + +RICHMOND, M. D. + + 1952. Head bobbing in reptiles. Herpetologica, 8:38. + +ROSENFELD, S., and GLASS, S. + + 1940. The inhibiting effect of snake bloods upon the hemorrhagic + action of viper venoms on mice. Amer. Jour. Med. Sci., + 199:482-486. + +SCHMIDT, K. P. + + 1946. On the zoogeography of the Holarctic region. Copeia, + 1946:144-152. + +SHAW, C. E. + + 1948. The male combat "dance" of some crotalid snakes. + Herpetologica, 4:137-145. + + 1951. Male combat in American colubrid snakes with remarks on + combat in other colubrid and elapid snakes. Herpetologica, + 7(4):149-168. + +SMITH, H. M. + + 1956. Handbook of amphibians and reptiles of Kansas. 2nd + Edition. Univ. Kansas Mus. Nat. Hist., Misc. Publ., 9:1-356, 253 + figs. + +SMITH, H. M., and BUECHNER, H. K. + + 1947. The influence of the Balcones Escarpment on the + distribution of amphibians and reptiles in Texas. Bull. Chicago + Acad. Sci., pp. 1-16. + +SMITH, P. W. + + 1961. The amphibians and reptiles of Illinois. Illinois Nat. + Hist. Survey, 28(1):1-298. + +SMITH, P. W., and LIST, J. C. + + 1955. Notes on Mississippi amphibians and reptiles. Amer. Midl. + Nat., 53(1):115-125. + +SOWDER, W. T., and GEHRES, G. W. + + 1963. Snakebites in Florida. Jour. Florida Med. Assn., + 49(12):973-976. + +STABLER, R. M. + + 1951. Some observations on two cottonmouth moccasins made during + 12 and 14 years of captivity. Herpetologica, 7:89-92. + +STAHNKE, H. M. + + 1953. The L-C treatment of venomous bites and stings. Amer. Jour. + Trop. Med. and Hyg., 2(1):142-143. + + 1954. The L-C method of treating venomous bites and stings. Pois. + Anim. Res. Lab., Arizona State Coll., 28 pp. + +STEJNEGER, L. + + 1895. The poisonous snakes of North America. Smithsonian Inst., U. + S. Nat. Mus., 1893:337-487, pls. 1-19, figs. 1-70. + +STIMSON, A. C., and ENGELHARDT, T. H. + + 1960. The treatment of snakebite. Jour. Occ. Med., 2(4):163-168. + +SUTHERLAND, I. D. + + 1958. The "combat dance" of the timber rattlesnake. Herpetologica, + 14(1):23-24. + +SWANSON, P. L. + + 1946. Effects of snake venoms on snakes. Copeia, 1946(4):242-249. + +SWAROOP, S., and GRAB, B. + + 1956. The snakebite mortality problem in the world. Pp. 439-466 + _in_ Venoms (ed. Buckley, E. E., and Porges, N., Amer. Assoc. Adv. + Sci., Publ. No. 44). + +SWARTZWELDER, J. C. + + 1950. Snake-bite accidents in Louisiana with data on 306 cases. + Amer. Jour. Trop. Med., 30(4):575-589. + +TINKLE, D. W. + + 1962. Reproductive potential and cycles in female _Crotalus atrox_ + from northwestern Texas. Copeia, 1962(2):306-313. + +TROWBRIDGE, A. H. + + 1937. Ecological observations on amphibians and reptiles collected + in southeastern Oklahoma during the summer of 1934. Amer. Midl. + Nat., 18(2):285-303. + +VOLSØE, H. + + 1944. Structure and seasonal variation of the male reproductive + organs in _Vipera berus_ (L.). Spolia Zool. Mus. Hauniensis V. + Reprint, Copenhagen, pp. 1-172. + +WHARTON, C. H. + + 1960. Birth and behavior of a brood of cottonmouths, _Agkistrodon + piscivorus piscivorus_, with notes on tail-luring. Herpetologica, + 16:125-129. + +WILLSON, P. + + 1908. Snake poisoning in the United States: a study based on an + analysis of 740 cases. Arch. Int. Med., 1(5):516-570. + +WOLFF, N. O., and GITHENS, T. S. + + 1939a. Record venom extraction from water moccasin. Copeia, + 1939(1):52. + + 1939b. Yield and toxicity of venom from snakes extracted over a + period of two years. Copeia, 1939(4):234. + +WOOD, J. T. + + 1954a. The distribution of poisonous snakes in Virginia. Virginia + Jour. Sci., 5(3):152-167, 4 maps. + + 1954b. A survey of 200 cases of snake-bite in Virginia. Amer. Jour. + Trop. Med. and Hyg., 3(5):936-943. + +WOOD, J. T., HOBACK, W. W., and GREEN, T. W. + + 1955. Treatment of snake venom poisoning with ACTH and cortisone. + Virginia Med. Month, 82:130-135. + +WRIGHT, A. H., and WRIGHT, A. A. + + 1957. Handbook of snakes of the United States and Canada. Comstock + Publ. Assoc., Cornell Univ. Press, 2:ix + 565-1106 pp. + +YAMAGUTI, S. + + 1958. Systema helminthum. Interscience Publ., Inc., New York, 3 + vols., 5 parts, 1:xi + 1575 pp., 2:vii + 860 pp., 3:1261 pp. + +YERGER, R. W. + + 1953. Yellow bullhead preyed upon by cottonmouth moccasin. Copeia, + 1953(2):115. + + _Transmitted June 20, 1966._ + + + + +UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY + + +Institutional libraries interested in publications exchange may obtain +this series by addressing the Exchange Librarian, University of Kansas +Library, Lawrence, Kansas. Copies for individuals, persons working in a +particular field of study, may be obtained by addressing instead the +Museum of Natural History, University of Kansas, Lawrence, Kansas. When +copies are requested from the Museum, 25 cents should be included (for +each 100 pages or part thereof) for the purpose of defraying the costs +of wrapping and mailing. For certain longer papers an additional amount +indicated below, toward the cost of production, is to be included. +Materials published to date in this series are as follows. + +* An asterisk designates those numbers of which the Museum's +supply (not necessarily the Library's supply) is exhausted. +Materials published to date, in this series, are as follows: + +Vol. 1. + + Nos. 1-26 and index. Pp. 1-638, 1946-1950. + +*Vol. 2. + + (Complete) Mammals of Washington. By Walter W. Dalquest. Pp. + 1-444, 140 figures in text. April 9, 1948. + +*Vol. 3. + + Nos. 1-4 and index. Pp. 1-681. 1951. + +*Vol. 4. + + (Complete) American weasels. By E. Raymond Hall. Pp. 1-466, 41 + plates, 31 figures in text. December 27, 1951. + +Vol. 5. + + Nos. 1-37 and index. Pp. 1-676, 1951-1953. + +*Vol. 6. + + (Complete) Mammals of Utah, _taxonomy and distribution_. By + Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables. + August 10, 1952. + +Vol. 7. + + Nos. 1-15 and index. Pp. 1-651, 1952-1955. + +Vol. 8. + + Nos. 1-10 and index. Pp. 1-675, 1954-1956. + +Vol. 9. + + Nos. 1-23 and index. Pp. 1-690, 1955-1960. + +Vol. 10. + + Nos. 1-10 and index. Pp. 1-626, 1956-1960. + +Vol. 11. + + Nos. 1-10 and index. Pp. 1-703, 1958-1960. + +Vol. 12. + + *1. Functional morphology of three bats: Eumops, Myotis, + Macrotus. By Terry A. Vaughan. Pp. 1-153, 4 plates, 24 figures + in text. July 8, 1959. + + *2. The ancestry of modern Amphibia: a review of the evidence. + By Theodore H. Eaton, Jr. Pp. 155-180, 10 figures in text. July + 10, 1959. + + 3. The baculum in microtine rodents. By Sydney Anderson. Pp. + 181-216, 49 figures in text. February 19, 1960. + + *4. A new order of fishlike Amphibia from the Pennsylvanian of + Kansas. By Theodore H. Eaton, Jr., and Peggy Lou Stewart. Pp. + 217-240, 12 figures in text. May 2, 1960. + + 5. Natural history of the Bell Vireo. By Jon C. Barlow. Pp. + 241-296, 6 figures in text. March 7, 1962. + + 6. Two new pelycosaurs from the lower Permian of Oklahoma. By + Richard C. Fox. Pp. 297-307, 6 figures in text. May 21, 1962. + + 7. Vertebrates from the barrier island of Tamaulipas, México. + By Robert K. Selander, Richard F. Johnston, B. J. Wilks, and + Gerald G. Raun. Pp. 309-345, plates 5-8. June 18, 1962. + + 8. Teeth of edestid sharks. By Theodore H. Eaton, Jr. Pp. + 347-362, 10 figures in text. October 1, 1962. + + 9. Variation in the muscles and nerves of the leg in two genera + of grouse (Tympanuchus and Pedioecetes). By E. Bruce Holmes. + Pp. 363-474, 20 figures. October 25, 1962. $1.00. + + 10. A new genus of Pennsylvanian fish (Crossopterygii, + Coelacanthiformes) from Kansas. By Joan Echols. Pp. 475-501, 7 + figures. October 25, 1963. + + 11. Observations on the Mississippi Kite in southwestern + Kansas. By Henry S. Fitch. Pp. 503-519. October 25, 1963. + + 12. Jaw musculature of the Mourning and White-winged doves. By + Robert L. Merz. Pp. 521-551, 22 figures. October 25, 1963. + + 13. Thoracic and coracoid arteries in two families of birds, + Columbidae and Hirundinidae. By Marion Anne Jenkinson. Pp. + 553-573, 7 figures. March 2, 1964. + + 14. The breeding birds of Kansas. By Richard F. Johnston. Pp. + 575-655, 10 figures. May 18, 1964. 75 cents. + + 15. The adductor muscles of the jaw in some primitive reptiles. + By Richard C. Fox. Pp. 657-680, 11 figures in text. May 18, + 1964. + + Index. Pp. 681-694. + +Vol. 13. + + 1. Five natural hybrid combinations in minnows (Cyprinidae). By + Frank B. Cross and W. L. Minckley. Pp. 1-18. June 1, 1960. + + 2. A distributional study of the amphibians of the Isthmus of + Tehuantepec, México. By William E. Duellman. Pp. 19-72, plates + 1-8, 3 figures in text. August 16, 1960. 50 cents. + + 3. A new subspecies of the slider turtle (Pseudemys scripta) + from Coahuila, México. By John M. Legler. Pp. 73-84, plates + 9-12, 3 figures in text. August 16, 1960. + + *4. Autecology of the copperhead. By Henry S. Fitch. Pp. + 85-288, plates 13-20, 26 figures in text. November 30, 1960. + + 5. Occurrence of the garter snake, Thamnophis sirtalis, in the + Great Plains and Rocky Mountains. By Henry S. Fitch and T. Paul + Maslin. Pp. 289-308, 4 figures in text. February 10, 1961. + + 6. Fishes of the Wakarusa River in Kansas. By James E. Deacon + and Artie L. Metcalf. Pp. 309-322, 1 figure in text. February + 10, 1961. + + 7. Geographic variation in the North American cyprinid fish, + Hybopsis gracilis. By Leonard J. Olund and Frank B. Cross. Pp. + 323-348, plates 21-24, 2 figures in text. February 10, 1961. + + 8. Descriptions of two species of frogs, genus Ptychohyla; + studies of American hylid frogs, V. By William E. Duellman. Pp. + 349-357, plate 25, 2 figures in text. April 27, 1961. + + 9. Fish populations, following a drought, in the Neosho and + Marais des Cygnes rivers of Kansas. By James Everett Deacon. + Pp. 359-427, plates 26-30, 3 figures. August 11, 1961. 75 + cents. + + 10. Recent soft-shelled turtles of North America (family + Trionychidae). By Robert G. Webb. Pp. 429-611, plates 31-54, 24 + figures in text. February 16, 1962. $2.00. + + Index. Pp. 613-624. + +Vol. 14. + + 1. Neotropical bats from western México. By Sydney Anderson. + Pp. 1-8. October 24, 1960. + + 2. Geographic variation in the harvest mouse, Reithrodontomys + megalotis, on the central Great Plains and in adjacent regions. + By J. Knox Jones, Jr., and B. Mursaloglu. Pp. 9-27, 1 figure in + text. July 24, 1961. + + 3. Mammals of Mesa Verde National Pork, Colorado. By Sydney + Anderson. Pp. 29-67, plates 1 and 2, 3 figures in text. July + 24, 1961. + + 4. A new subspecies of the black myotis (bat) from eastern + Mexico. By E. Raymond Hall and Ticul Alvarez. Pp. 69-72, 1 + figure in text. December 29, 1961. + + 5. North American yellow bats, "Dasypterus," and a list of the + named kinds of the genus Lasiurus Gray. By E. Raymond Hall and + J. Knox Jones, Jr. Pp. 73-98, 4 figures in text. December 29, + 1961. + + 6. Natural history of the brush mouse (Peromyscus boylii) in + Kansas with description of a new subspecies. By Charles A. + Long. Pp. 99-111, 1 figure in text. December 29, 1961. + + 7. Taxonomic status of some mice of the Peromyscus boylii group + in eastern Mexico, with description of a new subspecies. By + Ticul Alvarez. Pp. 113-120, 1 figure in text. December 29, + 1961. + + 8. A new subspecies of ground squirrel (Spermophilus spilosoma) + from Tamaulipas, Mexico. By Ticul Alvarez. Pp. 121-124. March + 7, 1962. + + 9. Taxonomic status of the free-tailed bat, Tadarida yucatanica + Miller. By J. Knox Jones, Jr., and Ticul Alvarez. Pp. 125-133, + 1 figure in text. March 7, 1962. + + 10. A new doglike carnivore, genus Cynaretus, from the + Clarendonian Pliocene, of Texas. By E. Raymond Hall and Walter + W. Dalquest. Pp. 135-138, 2 figures in text. April 30, 1962. + + 11. A new subspecies of wood rat (Neotoma) from northeastern + Mexico. By Ticul Alvarez. Pp. 139-143, April 30, 1962. + + 12. Noteworthy mammals from Sinaloa, Mexico. By J. Knox Jones, + Jr., Ticul Alvarez, and M. Raymond Lee. Pp. 145-159. 1 figure + in text. May 18, 1962. + + 13. A new bat (Myotis) from Mexico. By E. Raymond Hall. Pp. + 161-164, 1 figure in text. May 21, 1962. + + *14. The mammals of Veracruz. By E. Raymond Hall and Walter W. + Dalquest. Pp. 165-362, 2 figures. May 20, 1963. $2.00. + + 15. The recent mammals of Tamaulipas, México. By Ticul Alvarez. + Pp. 363-473, 5 figures in text. May 20, 1963. $1.00. + + 16. A new subspecies of the fruit-eating bat, Sturnira + ludovici, from western Mexico. By J. Knox Jones, Jr., and Gary + L. Phillips. Pp. 475-481, 1 figure in text. March 2, 1964. + + 17. Records of the fossil mammal Sinclairella, Family + Apatemyidae, from the Chadronian and Orellan. By William A. + Clemens. Pp. 483-491. 2 figures in text. March 2, 1964. + + 18. The mammals of Wyoming. By Charles A. Long. Pp. 493-758, 82 + figs. July 6, 1965. $3.00. + + Index. Pp. 759-784. + +Vol. 15. + + 1. The amphibians and reptiles of Michoacán, México. By William + E. Duellman. Pp. 1-148, plates 1-6, 11 figures in text. + December 20, 1961. $1.50. + + 2. Some reptiles and amphibians from Korea. By Robert G. Webb, + J. Knox Jones, Jr., and George W. Byers. Pp. 149-173. January + 31, 1962. + + 3. A new species of frog (Genus Tomodactylus) from western + México. By Robert G. Webb. Pp. 175-181, 1 figure in text. March + 7, 1962. 4. Type specimens of amphibians and reptiles in the + Museum of Natural History, the University of Kansas. By William + E. Duellman and Barbara Berg. Pp. 183-204. October 26, 1962. + + 5. Amphibians and Reptiles of the Rainforests of Southern El + Petén, Guatemala. By William E. Duellman. Pp. 205-249, plates + 7-10, 6 figures in text. October 4, 1963. + + 6. A revision of snakes of the genus Conophis (Family + Colubridae, from Middle America). By John Wellman. Pp. 251-295, + 9 figures in text. October 4, 1963. + + 7. A review of the Middle American tree frogs of the genus + Ptychohyla. By William E. Duellman. Pp. 297-349, plates 11-18, + 7 figures in text. October 18, 1963. 50 cents. + + *8. Natural history of the racer Coluber constrictor. By Henry + S. Fitch. Pp. 351-468, plates 19-22, 20 figures in text. + December 30, 1963. $1.00. + + 9. A review of the frogs of the Hyla bistincta group. By + William E. Duellman. Pp. 469-491, 4 figures in text. March 2, + 1964. + + 10. An ecological study of the garter snake, Thamnophis + sirtalis. By Henry S. Fitch. Pp. 493-564, plates 23-25, 14 + figures in text. May 17, 1965. + + 11. Breeding cycle in the ground skink, Lygosoma laterale. By + Henry S. Fitch and Harry W. Greene. Pp. 565-575, 3 figures in + text. May 17, 1965. + + 12. Amphibians and reptiles from the Yucatan Peninsula, México. + By William E. Duellman. Pp. 577-614, 1 figure in text. June 22, + 1965. + + 13. A new species of turtle, Genus Kinosternon, from Central + America, by John M. Legler. Pp. 615-625, pls. 26-28, 2 figures + in text. July 20, 1965. + + 14. A biogeographic account of the herpetofauna of Michoacán, + México. By William E. Duellman. Pp. 627-709, pls. 29-36, 5 + figures in text. December 30, 1965. + + 15. Amphibians and reptiles of Mesa Verde National Park, + Colorado. By Charles L. Douglas. Pp. 711-744, pls. 37, 38, 6 + figures in text. March 7, 1966. + + Index. Pp. 745-770. + +Vol. 16. + + 1. Distribution and taxonomy of Mammals of Nebraska. By J. Knox + Jones, Jr. Pp. 1-356, pls. 1-4, 82 figures in text. October 1, + 1964. $3.50. + + 2. Synopsis of the lagomorphs and rodents of Korea. By J. Knox + Jones, Jr., and David H. Johnson. Pp. 357-407. February 12, + 1965. + + 3. Mammals from Isla Cozumel, Mexico, with description of a new + species of harvest mouse. By J. Knox Jones, Jr., and Timothy E. + Lawlor. Pp. 409-419, 1 figure in text. April 13, 1965. + + 4. The Yucatan deer mouse, Peromyscus yucatanicus. By Timothy + E. Lawlor. Pp. 421-438, 2 figures in text. July 20, 1965. + + 5. Bats from Guatemala. By J. Knox Jones, Jr. Pp. 439-472. + April 18, 1966. + + More numbers will appear in volume 16. + +Vol. 17. + + 1. Localities of fossil vertebrates obtained from the Niobrara + Formation (Cretaceous) of Kansas. By David Bardack. Pp. 1-14. + January 22, 1965. + + 2. Chorda tympani branch of the facial nerve in the middle ear + of tetrapods. By Richard C. Fox. Pp. 15-21, May 22, 1965. + + 3. Fishes of the Kansas River System in relation to + zoogeography of the Great Plains. By Artie L. Metcalf. Pp. + 23-189, 4 figures in text, 51 maps. March 24, 1966. + + 4. Factors affecting growth and reproduction of channel + catfish, Ictalurus punctatus. By Bill A. Simco and Frank B. + Cross. Pp. 191-256, 13 figures in text. June 6, 1966. + + 5. A new species of fringe-limbed tree frog, genus Hyla, from + Darién, Panamá. By William E. Duellman. Pp. 257-262, 1 figure + in text. June 17, 1966. + + 6. Taxonomic notes on some Mexican and Central American hylid + frogs. By William E. Duellman. Pp. 263-279. June 17, 1966. + + 7. Neotropical hylid frogs, genus Smilisca. By William E. + Duellman and Linda Trueb. Pp. 281-375, pls. 1-12, 17 figures in + text. July 14, 1966. + + 8. Birds from North Borneo. By Max C. Thompson. Pp. 377-433, 1 + figure in text. October 27, 1966. + + 9. Natural history of cottonmouth moccasin, Agkistrodon + piscivorus (Reptilia). By Ray D. Burkett. Pp. 435-491, 7 + figures in text. October 27, 1966. + + More numbers will appear in volume 17. + + + + + +End of the Project Gutenberg EBook of Natural History of Cottonmouth +Moccasin, Agkistrodon piscovorus (Reptilia), by Ray D. 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