Cottonmouth
VenomousAgkistrodon piscivorus · also called water moccasin, swamp moccasin, gaper
The cottonmouth is North America's only semi-aquatic pit viper, and it is the snake behind most 'water moccasin' reports — nearly all of which are actually harmless water snakes. Its defensive display is unmistakable: it opens its mouth wide to show a startlingly white lining. That gape is a warning, not an attack, and it is the single most useful identification feature the species has.
Before anything else
- Back away and leave it alone. A snake that can see you leaving has no reason to bite. Most bites in the United States happen to people who picked up, cornered, or tried to kill a snake.
- Never handle a snake to identify it. Every identification on this site can be made from a photo or from several feet away.
- If someone is bitten, call emergency services now. Keep the limb still and below the heart, remove rings and watches, and go to hospital. Do not cut, suck, apply ice, or use a tourniquet — all of these make outcomes worse.
- Do not try to catch the snake for identification. A photo from a distance is enough, and hospitals treat symptoms rather than species.
In the US, the Poison Help line is 1-800-222-1222. This site is a reference, not medical advice.
Quick facts
- Venom
- Medically significant venom that is more destructive to tissue than a copperhead's. Bites require emergency care. Do not attempt to catch, kill or move one — a large share of bites in the United States happen while people are handling or attacking a snake.
- Adult length
- 26–60 inches (66–152 cm)
- Markings
- Young cottonmouths are boldly banded in brown and tan with a yellow tail tip. They darken with age, and large adults are often almost uniformly dark olive, brown or black with the pattern barely visible. A broad dark cheek stripe runs from the eye back along the jaw.
- Habitat
- water, wetland, woods
- Family
- pit viper
- Range
- 16 US states
How to identify a cottonmouth
- The open-mouth gape showing a cotton-white lining. No harmless North American water snake does this.
- Swims with the body riding high and buoyant on the surface. Water snakes swim mostly submerged with only the head showing.
- Broad dark band through and behind the eye, often bordered above and below by pale lines.
- When approached it usually stands its ground and coils rather than fleeing into the water.
What it does when it sees you
Cottonmouths are far less aggressive than their reputation suggests. Studies in which people deliberately stood near, stepped beside and even trod on wild cottonmouths found that the great majority tried to escape or bluffed with the gape, and only a small minority attempted to bite. They will not chase you.
What the cottonmouth is confused with
One test settles each of these.
Water snakes flee into the water and swim submerged; cottonmouths hold ground and float high. Water snakes never gape white.
Banded water snakes have round pupils, a slimmer head that flows into the neck, and no white mouth display.
Plain-bellied water snakes are uniformly dark on top like an old cottonmouth, but have a plain yellow or orange belly and no facial band.