The cottonmouth, Agkistrodon piscivorus, is a venomous snake native to the freshwater habitats of the Southeastern United States. Also known as the water moccasin, this species is a semi-aquatic viper, spending a significant portion of its life in or near water. This strong association with aquatic environments has led to a widespread misunderstanding regarding its ability to strike while submerged.
The Truth About Underwater Bites
A long-standing myth suggests that the cottonmouth cannot deliver a venomous bite while fully underwater. This is untrue; cottonmouths are fully capable of biting beneath the surface. Their jaw structure and specialized fangs are unimpaired by the surrounding water. The snake’s ability to strike is functionally the same whether it is on land or submerged.
Like all pit vipers, the cottonmouth possesses hinged fangs and powerful jaw muscles to quickly deploy its venom. The surrounding water slightly reduces the strike velocity compared to a terrestrial attack, but the mechanical action of injecting venom remains effective. This capability is necessary because much of the snake’s diet consists of aquatic prey captured while swimming or submerged.
The misconception stems from the fact that most snakes prefer not to bite defensively when underwater, choosing instead to flee or hide. However, if a cottonmouth is threatened or provoked while submerged, the venom delivery mechanism is fully functional. This confirms the cottonmouth as a true aquatic predator, not limited by its environment.
Aquatic Predation and Behavior
The cottonmouth functions primarily as an ambush predator in its aquatic surroundings. It prefers slow-moving bodies of water such as swamps, marshes, and drainage ditches, and is rarely found far from water. The snake hunts fish, amphibians, small mammals, and other reptiles, often waiting patiently for prey.
Juvenile cottonmouths employ caudal luring, using their brightly colored, yellowish tail tips to mimic an insect or worm. They wiggle the tail to attract prey, such as frogs, within striking range. Adults shift their foraging strategy, typically employing active hunting or scavenging along the water’s edge.
When swimming, the cottonmouth is distinct because its body often floats buoyantly on the water’s surface. This differs from many non-venomous water snakes, which swim with their bodies submerged just below the surface. If threatened, the cottonmouth displays a warning by coiling and opening its mouth wide to reveal the white interior, which gives it the common name. Bites on humans most frequently occur on land when the snake is accidentally stepped on or harassed.
Distinguishing Cottonmouths from Harmless Water Snakes
Misidentification is common because many non-venomous water snakes share the cottonmouth’s habitat, leading to unnecessary fear and harm to harmless species. Distinguishing the venomous cottonmouth from species like the Northern Water Snake (Nerodia sipedon) requires observing specific physical and behavioral cues.
Cottonmouths are pit vipers, characterized by a thick, triangular head that is noticeably wider than their neck. They possess heat-sensing facial pits located between the eyes and nostrils, and their pupils are vertical slits, resembling those of a cat. Non-venomous water snakes typically have a rounded head that is not much wider than the neck, and they have round pupils.
The way the snakes carry themselves in the water is another distinguishing feature. Cottonmouths usually swim with their entire body resting on the surface, appearing to float like a cork. Most water snakes swim with their head elevated, but the rest of their body is submerged just below the water line. The cottonmouth has a single row of scales under its tail, while water snakes have a double row.