MOCCASINS. Although they are found far into West Texas, both aquatic and terrestrial moccasins of the pit viper genus Agkistrodon are more numerous in the eastern third of the state, where they are generally the most abundant venomous serpents. The Viperidae, or pit vipers, which in the United States include rattlesnakes and moccasins, can be distinguished from nonvenomous snakes by the vertical slit of their pupils (nonvenomous serpents have round pupils) and by their pointed snout, triangular head, and undercut cheeks pocked with a dark heat-sensing pit between each eye and nostril. The pit enables the snake to locate and attack warm-blooded prey. The venom is primarily hemotoxic (or hemorrhagic), affecting blood cells and blood vessels, though some neurotoxic elements (affecting the nervous system) are included. Moccasins also have but a single row of belly scales behind the vent, where almost all nonvenomous snakes have a double row. The moccasins in Texas include the western cottonmouth and four subspecies of copperheads. The western cottonmouth (Agkistrodon piscivorus leucostoma) swims slowly, pausing frequently to float on the surface, while nonvenomous water snakes wriggle steadily forward with heads and necks above water, their bodies drooping into the water if they stop. The term water moccasin has been broadly used to refer to all water snakes, but only the cottonmouth is poisonous. Though young cottonmouths have distinct broad crossbands, the markings often become nondistinct against a darker background as the snake matures. Adult cottonmouths vary in color from dark brown to olive green to almost black and can reach a length of five feet, but most reach an average length of twenty to thirty inches.
Copperheads are plump-bodied, brown-banded, woodland snakes whose necks, when seen from above, are less than a third the thickness of their wedge-shaped heads. Their coloring provides a natural camouflage against ground covering and foliage. Adult copperheads generally reach a maximum length of eighteen to thirty inches. The four copperhead subspecies in Texas are much alike, with coloring and scalation that only gradually vary from east to west across the state. The southern copperhead (Agkistrodon contortrix contortrix) is a tan or pale-gray to pinkish eastern forest animal whose brown bands narrow (contortrix means "cinched" in Latin) over its spine. The northern copperhead (Agkistrodon contortrix mokasen) is a darker-shaded snake with wide, coppery, reddish-brown crossbands, and is found in Northeast Texas. The broad-banded copperhead (Agkistrodon contortrix laticinctus) of Central and North Texas has more uniformly wide, reddish-brown crossbands. The Trans-Pecos copperhead (Agkistrodon contortrix pictigaster) of the West Texas mountains is russet-hued and lives in shrubby desert and canyons, though it is usually found near springs and streams in these desert regions. It has darker and slightly more numerous belly scales. Because of its bold coloration, the Trans-Pecos copperhead appeals to reptile collectors and has been protected from capture in Texas since 1977.
Both the aquatic cottonmouth and the four terrestrial subspecies of copperhead often live in close proximity to man. Copperheads occur in wooded residential neighborhoods, but due to the snakes' comparatively mild temperament, human beings can often inadvertently reach or step within inches of a camouflaged snake without provoking its strike. Even the cottonmouth, despite its formidable appearance and nasty reputation, often chooses to flee or gape openmouthed in threat rather than to coil and strike. The snake's threatening gesture of exposing the white tissue of the inside of its mouth has earned its popular name. When startled, moccasins have been known to vibrate their tails against vegetation; they can also secrete a musk.
Few bites by either copperheads or cottonmouths involve snakes not first touched or molested. Agkistrodon venom is not especially powerful; not a single death resulted from 308 southern copperhead bites studied over a ten-year period. In the early 1980s the mortality rate for cottonmouth poisoning throughout the United States was less than one person a year. A cottonmouth bite can be serious, however, and the venom does contain more neurotoxins than that of copperheads and rattlesnakes. Local tissue destruction resulting from a moccasin bite sometimes causes the loss of a limb or digit, and small children are always at mortal risk. Symptoms include swelling, pain, and discoloration at the site of the bite, as well as weakness, nausea, diarrhea, and often shock.
Copperheads are usually found on a carpet of oak or elm leaves, though they also hunt in adjacent pastureland and can climb into bushes or trees. Cottonmouths are usually found in or near water because of the shelter and rich food supply of murky ponds and rivers, but they also do well in dry environments and may range far from permanent water. After heavy flooding along the coast, they may turn up practically anywhere in that region. Seasonal activity patterns of both aquatic and terrestrial moccasins are largely a function of prevailing temperature. They are generally active from March through December and have also been seen on warm days in January and February. They hibernate along hillsides and upland areas above streams, usually under large roots, in burrows, or in rock crevices. In spring and fall, snakes are most active during the warm part of the day, whereas in summer they are most active at dusk or after dark. They seek a variety of prey animals. Copperheads eat insects, mice, frogs, and small birds, and cottonmouths feed on frogs, fish, water snakes, eggs, lizards, and other small vertebrates.
Breeding occurs in early spring and sometimes fall; spermatozoa from the autumn pairings remains viable in the female's cloaca to fertilize the first ova she produces in spring. Litters are born alive in late summer and contain from one to approximately twenty, but on average include from three to twelve young, with yellow to grayish-chartreuse tail tips. The young snakes are able to hunt at once, sometimes using their tails, which resemble small insects or worms, to lure prey. They disperse within hours of their birth.
Bayard H. Brattstrom, "Evolution of the Pit Vipers," Transactions of the San Diego Society of Natural History 13 (1964). Roger Conant, A Field Guide to Reptiles and Amphibians of the United States and Canada East of the 100th Meridian (Boston: Houghton Mifflin, 1958; 2d ed., A Field Guide to Reptiles and Amphibians of Eastern and Central North America, 1975). Carl H. Ernst, Venomous Reptiles of North America (Washington: Smithsonian Institution Press, 1992). Kenneth V. Kardong, "Prey Capture in the Cottonmouth Snake," Journal of Herpetology 9 (1975). Wilfred T. Neill, "Size and Habits of the Cottonmouth Moccasin," Herpetologica 3, Pt. 6 (July 15, 1947). Alan Tennant, The Snakes of Texas (Austin: Texas Monthly Press, 1984). Alan Tennant, The Snakes of Texas: A Texas Monthly Field Guide (Austin: Texas Monthly Press, 1985). John E. Werler, Poisonous Snakes of Texas and First Aid Treatment of Their Bites (Bulletin 31, Austin: Texas Parks and Wildlife Department, February 1950). C. H. Wharton, "Birth and Behavior of a Brood of the Cottonmouth, Agkistrodon piscivorus piscivorus, with Notes on Tail-luring," Herpetologica 16 (March 31, 1960). Albert Hazen Wright and Anna Allen Wright, Handbook of Snakes of the United States and Canada (Vols. 1–2, Ithaca, New York: Comstock Publishing, 1957; Vol. 3, Ann Arbor, Michigan: Edwards Brothers, 1962).