15-55 inches. Dark tan, brown or nearly black, with vague black or dark brown crossbands; side of head black with a white line from the eye to the angle of the mouth; underside dark with large blackish blotches; scales keeled and in 25 rows. Juveniles have a bold pattern of dark brown crossbands on a pink or orange background, with a yellow tail. Some adults retain the juvenile pattern.
Cottonmouths frequent swamplands and pond, lake and stream borders, especially those with dense canopies. They often remain coiled near water, or on log jams in water, rarely ascending shrubs or palmettos. They frequently travel between streams, even over low ridges, and may be found in almost any habitat. Upon provocation, cottonmouths will coil, open their mouths to expose the white lining, and shake their tails. They are highly defensive and not inclined to get out of one's way. They feed on fish, frogs, water snakes and small mammals, and give birth to from 2-20 young.