Natural History of Cottonmouth Moccasin, Agkistrodon Piscovorus (reptilia)

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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)

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

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.

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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).

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