How to Identify the Water Moccasin (Identification Guide)

Key identifying features

The water moccasin (Agkistrodon piscivorus), commonly called the cottonmouth, is a heavy-bodied pit viper found throughout the southeastern United States. It is best recognized by its large, angular head that is distinctly wider than its neck, its thick muscular body, and its habit of swimming with much of its body riding on the surface of the water rather than submerged. When threatened, it often gapes its jaws widely to reveal the pale, cottony-white interior of its mouth, the source of its common name.

Coloration & pattern

Adults are typically olive, brown, or nearly black, often appearing so dark that the pattern is difficult to see. Younger individuals show a much clearer pattern of dark crossbands on a lighter tan or reddish-brown background, with bands that are wider on the sides and narrower across the back. As snakes age, the pattern frequently darkens and becomes obscured, so mature adults can look almost uniformly black or olive-brown. The belly is usually dark with scattered lighter blotches.

Head, eyes & scales

The head is large, blocky, and triangular, clearly set off from a narrower neck, a shape typical of pit vipers. A heat-sensing pit is located between each eye and nostril. The pupils are vertically elliptical (cat-like) in good light, though this can be hard to observe safely at a distance. Dark facial stripes running from the eye to the jaw are visible in juveniles and some adults but often fade with age. Body scales are strongly keeled, giving the skin a rough, dull texture rather than a glossy sheen.

Size & body shape

Water moccasins are stout, thick-set snakes, usually reaching 2 to 4 feet in length, with some large individuals exceeding this. The body is heavy for its length, tapering to a moderately short tail. Juveniles have a bright yellow or greenish tail tip used to lure prey, which fades as they mature.

Range & habitat where you'll see it

This species is found from Virginia south through Florida and west to Texas and southern Illinois. It is strongly associated with water, inhabiting swamps, marshes, slow-moving streams, lake edges, and drainage ditches. It is often seen basking on logs, banks, or floating vegetation near water, and swims with its head held up and much of its body visible on the surface.

How to tell it apart from look-alikes

Water moccasins are frequently confused with harmless water snakes (Nerodia species), which share aquatic habitats. Water snakes have narrower, more rounded heads, round pupils, slimmer bodies, and swim mostly submerged with only the head above water. Cottonmouths swim with more of the body floating on the surface. Juvenile cottonmouths can resemble copperheads due to banding, but copperheads have hourglass-shaped bands and are not typically found swimming in open water. The white mouth-gaping defensive display, when observed from a safe distance, is a distinctive behavioral clue unique to this species among North American snakes.