Facts About Water Moccasin (Cottonmouth) Snakes

Cottonmouth snake
Cottonmouth snakes, like all pit vipers, have heat-sensing pits on their faces, between their eyes and nostrils.
Credit: Rob Hainer | Shutterstock

North America’s only poisonous water snake, the water moccasin has a distinctive blocky triangular head, thick body and a dangerous bite. They rarely bite humans, however, and only attack when threatened. They are semi-aquatic, happy both swimming in water and basking on land in their native range of the Southeastern United States.

Water moccasin is a colloquial name for Cottonmouth snakes (Agkistrodonpiscivorus). The name"cottonmouth" comes from the pale inside of the snake’s mouth, which it exposes as a defensive display. Other local names for A. piscivorus includeblack moccasin, gaper, mangrove rattler, snap jaw, stub-tail snake, swamp lion, trap jaw, water mamba, and water pilot.

Cottonmouths are pit vipers, like copperheads and rattlesnakes. Pit vipers have heat-sensing pits on their faces, between their eyes and nostrils, which are able to detect minute differences in temperatures so that they can accurately strike the source of heat, which is often potential prey.

Young cottonmouth snake
Young cottonmouth snakes have striking patterns that fade with age.
Credit: Leighton Photography & Imaging | Shutterstock


Water moccasins are relatively large, often ranging from 2 to 4 feet long (61 to 121 centimeters). Their large, triangular heads are distinct from their thinner necks, unlike many other snakes that have no distinctive neck. They have large jowls, due to their venom glands, and “cat-eye” pupils. Water moccasins have dark stripes by each nostril and pale snouts, which can be helpful in identifying features.

Their thick, muscular bodies are stout for their length and covered in keeled, or ridged, scales. Their coloration varies from dark brown or black to olive, banded brown or yellow. Bellies are paler than backs. Young water moccasins have striking patterns of dark-bordered bands and pale centers and yellow tail tips, which they use as bait for fish and frogs. Their patterns fade or are lost as they age. 

Water moccasins are often confused with non-venomous snakes, leading to the death of many a harmless snake. Nonvenomous snakes typically have more slender bodies and sleek heads. Furthermore, the water moccasin’s eyes do not protrude and are not visible if one is looking down at the top of the snake.

Water moccassin eats a bullfrog, snakes
A water moccasin eats a bullfrog. The snake's diet consists of fish, small mammals, birds and amphibians; reptiles such as lizards, baby alligators and turtles; and other snakes, including smaller water moccasins.
Credit: Paul S. Wolf | Shutterstock


Water moccasins live in the Southeastern United States from southern Virginia to Florida to eastern Texas. There are three subspecies: western, Florida, and eastern cottonmouths.

Water moccasins may be found swimming in swamps, marshes, drainage ditches, and at the edges of ponds, lakes, and streams. On land, they’re found near water and fields. They like to sun themselves on branches, stones and logs near the water’s edge. Basking keeps up their body temperature, which chills quickly in water.


Water moccasins swim close to the top of the water with their heads out. They can be seen year-round, both during the day and at night, but they primarily hunt after dark, especially in the summer. Water moccasins eat fish, small mammals, birds, amphibians; reptiles such as lizards, baby alligators and turtles; and other snakes, including smaller water moccasins.

Water moccasins mate in early summer, after the males fight for females. Water moccasins are ovoviviparous, which means that eggs incubate inside the mother’s body. Females give birth to live young every two to three years, in litters of up to 20 babies. The gestation period lasts three to four months. Babies are born brightly colored and take off on their own as soon as they’re born. Parents do not care for them.

Though in reality they rarely bite humans, water moccasins have an aggressive reputation. Unlike many nonvenomous water snakes that flee from threats, water moccasins will stand their ground. They coil their bodies, open their mouths, expose their fangs, and gape at the threat in an attempt to scare it off. 


Water moccasins have hemotoxic venom, which works by breaking down and destroying tissues and blood cells, reducing the blood’s ability to coagulate or clot. This can cause hemorrhages throughout the circulatory system. Water moccasins’ bites are extremely painful and can be fatal, though very few humans have died from it. Antivenom is available, and about half of the bites from all venomous snakes are “dry,” meaning that no venom is actually secreted. Anyone suffering from a water moccasin bite should seek medical attention immediately.

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