Cottonmouth
Agkistrodon piscivorus · Water Moccasin
North America’s only semi-aquatic viper, named for the stark white lining it flashes as a warning. Here is how to tell it from a harmless water snake, and what its defensive display actually means.
How to Recognize a Cottonmouth
Adults typically run 2–4 ft, with exceptionally large individuals occasionally exceeding 5–6 ft. Heavy-bodied, with a broad triangular head distinctly wider than the neck.
The White Mouth
When threatened, it gapes its jaw wide to display a bright white or pinkish mouth lining — the source of both its common names. This is a defensive warning display, not an attack.
Darkens With Age
Juveniles are boldly banded on a lighter background with a bright yellow-green tail tip. Adults darken considerably, often ending up nearly uniform olive, brown, or black with the banding faded or gone entirely — a very different look from the pattern most people expect.
Swims With Its Head Up
The only semi-aquatic viper in North America. It swims with its head and much of its body riding on the surface, unlike harmless water snakes, which typically swim with just the head above water.
Widely mistaken for harmless water snakes. Non-venomous water snakes are common in the same habitat and are killed in large numbers by people who assume any snake in the water is a cottonmouth. Head shape and swimming posture are more reliable than color alone.
Where It Lives
Native to the southeastern US, from southeastern Virginia south through all of Florida and west through southern Alabama, Mississippi, Louisiana, eastern Texas, and parts of Arkansas and Oklahoma.
Strongly tied to freshwater: slow-moving streams, swamps, marshes, lake edges, and drainage ditches. It occasionally enters brackish water and has been recorded swimming between barrier islands and the mainland.
Defensive, Not Aggressive
Cottonmouths have a reputation for aggression that doesn’t match what wildlife agencies actually document. They bite when threatened or handled, the same as most venomous snakes — they just happen to stand their ground more than many species instead of fleeing.
The Gape Is a Warning
Coiling, tail-vibrating, and mouth-gaping are all defensive displays meant to avoid a bite, not provoke one. A cottonmouth that stands its ground and shows you its mouth is telling you to back away — heed it, and it will typically let you.
Real but Limited Risk
Its hemotoxic venom causes genuine tissue damage and every bite needs medical treatment, but cottonmouths account for a small share of US snakebite deaths — roughly 1% by some estimates, far below rattlesnakes.
The real risk is where you wade, not what it does
Most bites happen when a foot or hand lands somewhere a snake already was in murky water — not from an unprovoked strike.
Common Questions
Not by wildlife agency accounts. They bite when threatened or handled, like most venomous snakes, but stand their ground more than many species instead of fleeing. The mouth-gaping display that gives it its name is a defensive warning, not the start of an attack.
Wading or Working Wetlands?
A snake that can bite underwater changes what you actually need from your gear — standard fabric performs differently once it’s wet.
Waterproof Gaiters Guide
Built for wading, not just dry trails.
Back to Big Four Overview
Compare against rattlesnakes, copperheads, and coral snakes.