Can Cottonmouths Bite Underwater? Water Moccasin Myths

How cottonmouths bite underwater

The cottonmouth is one of the few vipers that lives mainly in and around water, and its scientific name, Agkistrodon piscivorus, means “hook-toothed fish-eater”. Fish and frogs make up most of its diet, and many of these meals are caught in the water.

A snake does not need air to bite. Its fangs fold forward and inject venom through muscle pressure on the venom glands, which works just as well below the surface as above it. Like other snakes, a cottonmouth can close off its windpipe while its mouth is open, so water does not flood its lungs.

That said, cottonmouths are not especially good at catching fish in open water. Observers have noted that they often fail when they try to seize fish underwater. Their favorite tactic is to corner fish in shallow water, against the bank or under logs and roots, and strike there. They do especially well in late summer, when ponds and ditches shrink and fish and tadpoles become trapped in small pools.

How do cottonmouths swim?

Cottonmouths are strong swimmers. Like other snakes, they swim by throwing their bodies into side-to-side curves that push against the water. What makes them distinctive is their posture.

A swimming cottonmouth usually floats high on the surface, with much of its body visible and buoyant, and it often holds its head raised at an angle. Many harmless water snakes swim lower in the water, with mainly the head and neck showing. This difference can help with identification at a distance, but it is not a perfect test, because a water snake can float and a cottonmouth can dive.

Cottonmouths also dive when they need to. A disturbed snake may slip under the surface and hide among plants or under a log for several minutes or longer. Snakes use oxygen slowly, particularly in cool water, so they can stay down much longer than a mammal of the same size. More about how snakes move in water is in Can snakes swim?.

They are not limited to fresh water. Cottonmouths live in brackish coastal marshes and have been seen swimming between barrier islands and the mainland, although they are not very salt-tolerant and need fresh water to drink.

Myth: moccasin nests that attack swimmers

One of the most famous snake legends in the American South tells of a water-skier or swimmer who falls into a “nest of water moccasins” and is bitten many times. Versions of this story have circulated for decades, often set at a lake or river that the storyteller names. Snake experts have found no documented case behind it.

The legend fails on basic biology. Cottonmouths do not build nests, and they do not live in groups that defend a patch of water. Several snakes may gather at a pool full of trapped fish, or share a winter den on higher ground, but each one acts independently. In open, deep water, a cottonmouth’s instinct is to escape, not to attack a large animal.

Other myths are just as widespread. Cottonmouths do not chase swimmers or boats; a snake swimming toward a person is usually heading for the bank, a basking log or cover, or has not noticed them. Field tests in South Carolina found that wild cottonmouths usually tried to flee or gave a threat display rather than biting; see Are cottonmouths aggressive?.

Is it dangerous to swim where cottonmouths live?

Cottonmouths live only in the southeastern and south-central United States, from southeastern Virginia to Florida and west to central Texas and Oklahoma. In the northern states and Canada, a snake in the water is almost always a harmless species such as the northern water snake.

Even in the South, bites in the water are very rare. Most cottonmouth bites happen on land or at the water’s edge, when people step on, sit on or reach toward a snake they did not see, or when they try to handle or kill one. A few simple habits reduce the risk:

• Swim in open, clear areas rather than in weedy shallows, flooded timber or around logs.
• Look before you step or put your hands along banks, docks, stumps and fallen trees.
• Never try to catch, move or kill a snake in or out of the water.
• Give any snake you see plenty of room; it will move away if it can.

A cottonmouth bite causes severe pain and swelling and is always a medical emergency, although deaths are very rare in the United States. If anyone is bitten, call 911 (US) and seek emergency medical help immediately.

Why the myths matter

Myths about killer moccasins lead people to kill many snakes, and most of the victims are harmless water snakes, which help keep wetland food webs in balance. Understanding how cottonmouths really behave in water, as shy, opportunistic hunters of fish and frogs, makes encounters safer for both people and snakes.