Cottonmouth Snake

Agkistrodon piscivorus

Agkistrodon piscivorus is a venomous snake, a species of pit viper, found in the eastern United States. Adults are large and capable of delivering a painful and potentially fatal bite.  This is the world's only semi-aquatic viper, usually found in or near water, particularly in slow-moving and shallow lakes and streams. The snake is a strong swimmer and will even enter the sea, successfully colonizing islands off both the Atlantic and Gulf coasts. The common names for the species include variants on water, swamp or black 'moccasin', 'viper', 'cottonmouth' and 'rattler'.  Many of the common names refer to the threat display, where this species will often stand its ground and gape at an intruder, exposing the white lining of its mouth.

The diet consists mainly of fish and frogs, but is otherwise highly varied and, uniquely, has even been reported to include carrion. The specific name is derived from the Latin words piscis and voro, which mean "fish" and "to eat". Three subspecies are currently recognized, including the nominate subspecies described here.


Though the majority of specimens are almost or even totally black, (with the exeption of head and facial markings) the color pattern may consist of a brown, gray, tan, yellowish olive or blackish ground color, which is overlaid with a series of 10-17 crossbands that are dark brown to almost black. These crossbands, which usually have black edges, are sometimes broken along the dorsal midline to form a series of staggered half bands on either side of the body. These crossbands are visibly lighter in the center, almost matching the ground color, often contain irregular dark markings, and extend well down onto the ventral scales. The dorsal banding pattern fades with age, so that older individuals are an almost uniform olive brown, grayish brown or black. The belly is white, yellowish white or tan, marked with dark spots, and becomes darker posteriorly. The amount of dark pigment on the belly varies from virtually nothing to almost completely black. The head is a more or less uniform brown color, especially in A. p. piscivorus. Subadult specimens may exhibit the same kind of dark, parietal spots that are characteristic of A. contortrix, but sometimes these are still visible in adults. Eastern populations have a broad dark postocular stripe, bordered with pale pigment above and below, that is faint or absent in western populations. The underside of the head is generally whitish, cream or tan.