Are Cottonmouths Aggressive? What Field Studies Show

What did the field studies find?

The best-known test of cottonmouth behavior was carried out by J. Whitfield Gibbons and Michael Dorcas of the Savannah River Ecology Laboratory in South Carolina, and published in the journal Copeia in 2002. They wanted to measure how wild cottonmouths actually react when a person meets them, rather than rely on folklore.

The researchers found 45 cottonmouths in the field and tested them with a series of encounters of increasing intensity. First a person simply stood next to the snake. Then the person stepped on it, wearing thick protective boots. Finally, the snake was picked up in the middle of the body with a pair of snake tongs fitted with a fake hand, which mimics someone grabbing it.

The results were striking:

In other words, the snakes overwhelmingly chose to flee or warn. Even the most extreme provocation, being grabbed, led to a bite in only about a third of cases. The authors concluded that cottonmouths are not aggressive and that most bites are the result of people handling or accidentally stepping on snakes.

Why do cottonmouths seem aggressive?

The main reason is the cottonmouth’s defense strategy. Many snakes, including harmless water snakes, dash for cover when disturbed. A cottonmouth often stays where it is, coils its body, vibrates its tail, hisses and throws its head back with its mouth wide open. This shows off the white lining of the mouth, which you can read about in Why is it called a cottonmouth?.

To a startled person, a snake that does not run away and opens its mouth looks like it is about to attack. In fact, the display is a warning signal. A venomous snake that advertises itself has a good chance of being left alone without ever needing to bite, which saves venom and avoids injury. Some cottonmouths also release a strong, goat-like musk from glands near the tail, another way of saying “leave me alone”.

Cottonmouths are also heavy, slow-moving snakes that rely partly on camouflage. A snake that cannot sprint away quickly gains more from a bold display than from a slow escape attempt.

The “chasing snake” myth

Stories of cottonmouths chasing people, swimming after boats or dropping into canoes are common across the South. Researchers have found no evidence that cottonmouths pursue people.

There are simpler explanations for these encounters. When a cottonmouth is disturbed, it heads for the nearest safe place, such as the water, a hole or a tangle of roots. If the person happens to stand between the snake and that refuge, the snake moves toward them, and it can look like a charge. Cottonmouths also swim with their heads raised, which looks more purposeful than the low-profile swimming of other snakes. A snake swimming toward a boat or swimmer is usually heading for a basking spot or the bank, or simply has not noticed the person.

Many “aggressive moccasin” stories also involve the wrong snake. Harmless water snakes are far more common in many areas and are often called moccasins. They bite readily when grabbed, which adds to the confusion; see cottonmouth vs water snake.

Which factors make a bite more likely?

Studies of cottonmouth defense suggest that a few factors raise the chance of a strike. Larger snakes were more likely to bite than smaller ones in some tests, and snakes that were already stressed, with higher levels of stress hormones, were also more likely to strike. Temperature matters too: cold snakes are sluggish and may rely more on staying still and displaying.

For people, the key factor is contact. Most venomous snakebites in the United States happen when someone tries to handle, move or kill a snake, or steps on or reaches near one without seeing it. Cottonmouths often rest in leaf litter, on logs and along banks, where their dark color makes them hard to spot.

How dangerous is a cottonmouth bite?

A cottonmouth bite is a serious medical emergency, even though deaths are very rare. The venom mainly damages tissue and interferes with blood clotting. It causes severe pain and swelling, and can lead to lasting injury. Antivenom is widely available in US hospitals.

The best protection is simple. Watch where you step and put your hands near water, logs and thick vegetation, wear sturdy footwear in swamps, and never try to touch or kill a snake. If you meet a cottonmouth, back away slowly and give it room. If anyone is bitten, call 911 (US) and seek emergency medical help immediately. You can find more about other species in venomous snakes in the US.

Respect, not fear

Cottonmouths deserve respect because they are venomous, but they are not hunters of people. Their threat display is a clear, honest warning that gives you time to step back. Seen from a safe distance, a cottonmouth gaping on a log is one of the most memorable sights of a southern swamp.