The water moccasin is venomous, not poisonous, though the two words are often used interchangeably in everyday conversation. The distinction matters: a poisonous animal harms you when you touch or ingest it, while a venomous animal injects toxin through a bite or sting. The water moccasin, also called the cottonmouth, delivers venom through hollow fangs and is one of only a handful of venomous water-dwelling snakes in North America. Its bite can cause serious tissue damage and requires emergency medical treatment, but deaths are rare.
How Dangerous Is a Bite?
Cottonmouth venom destroys tissue around the bite site. Swelling, pain, and discoloration typically begin within minutes and can spread rapidly up the affected limb. Without treatment, the venom can cause significant muscle and skin damage. In severe cases, it affects blood clotting throughout the body.
Across all venomous snake species in the United States, roughly 7,000 to 8,000 people are bitten each year, and only about five of those bites are fatal. Cottonmouth bites make up a fraction of that total. The modern antivenom used for pit viper bites (the family that includes cottonmouths, copperheads, and rattlesnakes) has been the standard since 2000. It is specifically designed for North American pit vipers and causes fewer allergic reactions than older treatments. In one pediatric study, no patients who received the antivenom needed surgery or blood products.
Are Cottonmouths Actually Aggressive?
Water moccasins have a reputation for chasing people, but controlled research tells a different story. In one study that directly confronted wild cottonmouths with a human presence, 51% of the snakes tried to escape rather than stand their ground. When the researchers pushed further and presented an artificial hand, only 13 out of 36 snakes actually bit it. Most relied on threat displays instead: coiling up, vibrating their tails, and gaping their mouths wide open to reveal a bright white or pinkish interior. That mouth display is where the name “cottonmouth” comes from, and it is a warning, not an attack.
Bites usually happen when someone accidentally steps on or grabs a snake they didn’t see, or when someone tries to handle or kill one. Giving the snake space is the simplest way to avoid a bite.
Where Water Moccasins Live
Cottonmouths are semiaquatic snakes found across the southeastern United States. Their range stretches from southeastern Virginia down through the Carolinas, Georgia, and all of Florida (including the upper Keys), then west through Alabama, Mississippi, Louisiana, Arkansas, eastern Texas, and Oklahoma. They also reach into southern Missouri, western Kentucky and Tennessee, and the extreme southern edges of Illinois and Indiana.
You’ll find them near slow-moving water: swamps, marshes, drainage ditches, lake edges, and floodplain forests. They hunt both in water and on land, often waiting motionless to ambush fish, frogs, and small mammals. If you spend time near freshwater in the Southeast, cottonmouths are part of the landscape.
How to Tell a Cottonmouth From a Harmless Water Snake
Most snakes you see swimming in southern waterways are nonvenomous water snakes, particularly the northern water snake. The two are easy to confuse at a glance, but several differences stand out once you know what to look for.
- Head shape: Cottonmouths have a flat, angular head that is noticeably wider than the neck. Water snakes have a more rounded head, though they sometimes flatten it when scared, mimicking the triangular look.
- Body color: Cottonmouths tend toward dark green or nearly black with dark brown hourglass-shaped bands. Northern water snakes are brown to gray with blotchy crossbands and flecks of red, yellow, or white.
- Facial pits: Cottonmouths have small heat-sensing pits between the eyes and nostrils. These are visible at close range but obviously not something you want to check in person.
- Swimming style: Cottonmouths float on the water’s surface with their bodies visible. Water snakes swim with most of their body submerged, just below the surface.
- Climbing: Cottonmouths are heavy and rarely climb more than a few feet off the ground. If you see a thick snake basking 10 or 20 feet up in a tree overhanging water, it is almost certainly a nonvenomous water snake.
When in doubt, keep your distance. The safest identification is the one you make from several feet away.
What to Do if You’re Bitten
Call 911 immediately. While waiting for help, move away from the snake and stay as still and calm as possible. Remove rings, watches, and tight clothing from the affected limb before swelling starts. Sit or lie down so the bite is at a comfortable, neutral position. Clean the wound with soap and water, then cover it loosely with a clean bandage.
What not to do is equally important. Do not apply a tourniquet or ice. Do not cut the bite wound or try to suck out venom. Do not take aspirin, ibuprofen, or naproxen, as these can interfere with blood clotting and make the effects of the venom worse. Skip caffeine and alcohol as well. The goal is to stay calm, limit movement, and get to a hospital where antivenom can be administered. Most people who receive prompt treatment recover without lasting damage.