Cottonmouth Water Moccasin

(Agkistrodon piscivorus)

by Jay Sharp


Cottonmouth, probably a juvenile as its markings are still very visible.

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The cottonmouth water moccasin -- the only venomous semiaquatic snake in the United States and the only semiaquatic pit viper in the United States -- holds broad residency in watery habitats across the southeastern quarter of the country. It occurs as one of three subspecies, including eastern, Florida and western cottonmouths.

Cottonmouth Characteristics

The mature adult cottonmouth has a roughly triangular-shaped and pale-snouted head, a narrow neck, and a comparatively heavy body, much like its taxonomic relatives, the rattlesnakes and the copperheads:

  • Size and Weight: The typical mature adult cottonmouth measures two to four feet in length, and it weighs three to four pounds. The male is somewhat larger than the female, occasionally exceeding six feet in length.

  • Head: Like its pit viper kin, the cottonmouth has heat-sensing pit-like organs on each side of its head, between the eye and the nostril. It has elliptical-shaped pupils, unlike the non-poisonous water snakes, which have circular pupils. It has a fork-shaped tongue, which it uses in the detection of odors in the air. In the front of its mouth, it has hollow fangs that serve for delivering venom from special glands located near the junctures of the jaws. When it opens its mouth, gaping, it displays a unique cotton-white lining (hence the snake's name) that serves as a warning flag to would-be predators.

  • Body: The cottonmouth has a thick body but a relatively long and slender tail. Coloring can vary widely: although a mature adult may retain some patterning, it typically has a dark black- or olive-colored back and a pale belly, according to the Smithsonian Natural Zoological Park. A young cottonmouth, by comparison, has, on its body, distinctive cross bands defined by dark borders and pale centers, and it has, on its tail, a tip marked by a bright yellow or greenish gray color. It may resemble its relative, the copperhead.

  • Senses: The cottonmouth has several important senses that help it in hunting and surviving. Its heat-sensing organs can detect temperature differences of less than two degrees Fahrenheit, alerting the snake to the presence of prey, especially at night, says the Smithsonian. Its forked, odor-detecting tongue help the snake track down any animal that flees after suffering a bite that is not immediately fatal. Its elliptical-shaped pupils facilitate seeing in the dim light of the night. Its belly muscles can detect ground vibrations produced by the larger animals, which could present a potential threat. Based on recent research, it seems to have hearing sufficient to detect moderate sounds of nearby origin.

  • Venom: Like its pit viper relatives, the cottonmouth's venom is "hemotoxic," which means that it destroys blood cells and associated tissues and that it reduces blood coagulation. The snake can deliver a bite, injecting its venom, on land or in the water.

The Three Subspecies (according to Roger Conant, A Field Guide to Reptiles and Amphibians of Eastern and Central North America):

  1. The mature eastern cottonmouth normally ranges from two and one-half to four feet in length but it may measure up to six feet. Older adults "may be completely dark and unpatterned."

  2. The mature Florida cottonmouth, similar in size to the eastern cottonmouth, has "conspicuous head markings--even in most large, dark individuals. A dark brown cheek stripe bordered above and below by a narrow light line.."

  3. The mature western cottonmouth, somewhat smaller, darker and less well patterned than either the eastern or Florida subspecies, is, in many instances, "plain black or dark brown with little or no trace of a pattern."

Distribution, Habitat and Diet

The cottonmouth's range, according to Conant, extends from the Atlantic coast to central Texas, across the southeastern quarter of the country. The eastern cottonmouth subspecies occurs from eastern Alabama northeastward to the Chesapeake Bay; the Florida cottonmouth, from the keys northward to southern Alabama and southern Georgia; and the western cottonmouth, from the central Gulf coast northward to southern Illinois, westward into Texas and Oklahoma, and eastward into Alabama and Georgia.

The cottonmouth, as a semiaquatic snake, favors the "swamps, streams, marshes, and drainage ditches in the southern lowlands of the United States," said the Smithsonian. "They also live at the edges of lakes, ponds, and slow moving streams and waters." The snake, laying claim to a territory of perhaps two to three acres, often makes its home along shorelines in heavy vegetation or beneath branches or fallen logs. A strong swimmer, the cottonmouth has crossed salt water to colonize islands along both the Gulf and Atlantic coasts.

As a semiaquatic snake, the cottonmouth feeds opportunistically on a diversity of both warm and cold-blooded wildlife of the Southeastern wetlands, including, especially, fish, frogs, young turtles and other semiaquatic snakes (including other cottonmouths). It also preys on small mammals, various birds, eggs, insects and carrion. When the cottonmouth strikes prey, it injects venom into the victim's tissues. It may grasp the prey in its coils until struggling ceases. It swallows mammals head first, detaching its jaw bones so it can open its mouth wide enough to accommodate the passage.

Behavior and Life Cycle

Although the generally solitary cottonmouth may be found any time of day, often basking on rocks or logs, it forages primarily at night, especially during the higher temperatures of summer. It may either ambush or actively hunt its prey. Threatened by a potential predator, the snake will often coil and "stand its ground," vibrating its tail, opening its cotton-white mouth, displaying its fangs, and emitting a foul-smelling odor to ward off an attack. Although it has a reputation for aggressiveness, it seldom bites if left alone, according to the Savannah River Ecology Laboratory. In fact, says Texas Parks & Wildlife, "Throughout the United States, less than 1% of all deaths by snakebite have been caused by cottonmouths." (Nevertheless, anyone suffering a bite by a cottonmouth should seek prompt medical attention.)

The cottonmouth mates during the spring, with the male reaching sexual maturity at about two years of age and the female, at about three years, according to Texas Parks & Wildlife.

The male may fight with other males to establish breeding rights. It performs a ritual "dance" to attract a female. Breeding begins with "the male nudging the female's back and sides. This continues for as long as several hours, until she exposes her tail and opens her cloaca [the opening to her genital tract] for copulation," said the Smithsonian.

After a gestation period of several months, the female delivers a litter of perhaps eight to twelve live young, each some eight to ten inches long, brightly patterned and colorfully tailed. She now regards her work as done. She promptly abandons the young snakes to fend for themselves. With ovulation occurring only every two years, she will not deliver another brood for some time.

The young cottonmouth, born with totally functional fangs and a full venom supply, comes prepared to hunt prey and defend itself. It may vibrate its brightly colored tail to mimic a worm and attract prey such as small frogs. If it reaches maturity, it will have a lifespan of less than ten years, according to the Texas Parks & Wildlife.

The Cottonmouth's Perils

The young cottonmouth lives in a perilous world, where it may serve as a meal to a number of predators, including, for instance, the longnose gar, the largemouth bass, snapping turtles, raccoons, dogs, cats, egrets, herons, hawks and eagles. The mature cottonmouth, given its size and defenses, faces far fewer threats, but even a large one may become occasional prey, for example, for an alligator. Juvenile and mature cottonmouths both face the dangers raised by humans, who not only kill the snake but also destroy its habitat. For all the perils, however, "There is no particular concern about the conservation of the cottonmouth," says the Smithsonian.

Interesting Facts

  • Distinctively, the cottonmouth swims "corklike," with its body seeming to merely skim the surface of the water.

  • During drought, cottonmouths sometimes cluster around dwindling pools of water to feed on trapped fish and amphibians, said the Savannah River Ecology Laboratory.

  • When the cottonmouth vibrates its tail in dry vegetation, it may produce a rattle, sounding much like a rattlesnake.

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