Cottonmouth Snake
The cottonmouth (Agkistrodon piscivorus), also known as the water moccasin, is the only semiaquatic viper in North America. It belongs to the pit viper family and lives in the southeastern United States, from southeastern Virginia and Florida west to eastern Texas and Oklahoma and north up the Mississippi valley to southern Illinois. Adults are heavy bodied with a broad, blocky head and keeled scales, and many turn dark brown to nearly black with age. The inside of the mouth is bright white, and the snake gapes it wide as a warning when it feels threatened. Its venom is mainly cytotoxic, destroying tissue, and a bite demands prompt medical attention, though deaths are very rare. The cottonmouth is an opportunistic hunter that eats fish, frogs, snakes, small mammals, birds and even carrion. It lives in and around swamps, marshes, creeks, river floodplains and ditches, and is active both by day and at night.
What is a cottonmouth snake?
The cottonmouth (Agkistrodon piscivorus), also called the water moccasin, is a venomous pit viper from the southeastern United States and the only semiaquatic viper in North America. It belongs to the same genus as the copperhead, and like all pit vipers it has a heat sensing pit on each side of the face, between the eye and the nostril, that lets it detect warm blooded animals in the dark. Its scientific name means "hook toothed fish eater". The name cottonmouth comes from its famous threat display: when cornered, it opens its mouth wide to show a lining as white as cotton. Other common names include swamp moccasin, black moccasin and simply moccasin, and many herpetologists avoid "water moccasin" because people use it for any snake they see in water, including harmless water snakes. Science has also changed its view of the species. A DNA study published in 2014 found that cottonmouths of the Florida peninsula are a separate species, the Florida cottonmouth (Agkistrodon conanti), while the eastern and western forms were merged into one. Both look and behave almost the same, and both are covered on this page.
How to identify a cottonmouth
Telling a cottonmouth from a harmless water snake is the question most people have, and a few features help. Cottonmouths are heavy bodied snakes with a broad, blocky head that is clearly wider than the neck, a heat sensing pit between the eye and the nostril, and, in eastern populations, a broad dark stripe running back from the eye. Their scales are keeled, giving the skin a rough look. Adults usually measure 65 to 90 centimeters, often more than 80, and the record is about 1.89 meters. Many older adults are almost or entirely black, while others show 10 to 17 dark crossbands over a brown, olive, gray or tan background, a pattern that fades with age. The belly is white, yellowish or tan with dark blotches. Behavior is often the best clue. A cottonmouth swims with its whole body floating high on the surface and its head held up at about 45 degrees, while water snakes of the genus Nerodia usually swim with the body below the surface. When threatened, a cottonmouth tends to hold its ground, coil and gape to show its white mouth. Water snakes have round pupils, no facial pit and a slimmer head, but those details are best checked from a safe distance or in a photo.
Where are cottonmouth snakes found?
Cottonmouths live only in the United States. Their range starts at the Great Dismal Swamp in southeastern Virginia and runs south through the Carolinas, Georgia and the whole Florida peninsula, then west across Alabama, Mississippi, Louisiana and Arkansas to eastern and southern Oklahoma and the eastern half of Texas. Up the Mississippi valley they reach western Kentucky and Tennessee, southern Missouri and the southern tips of Illinois and Indiana, where they are rare. Many barrier islands along the Atlantic and Gulf coasts also have them. Florida is one of their great strongholds, home to the Florida cottonmouth, and they are common in the wetlands of East Texas and Louisiana. Cottonmouths are tied to water, but not to any one kind: they live in creeks, streams, cypress swamps, marshes, river floodplains, the shores of ponds and lakes, and drainage ditches and canals. They can enter brackish water near the coast, though they do not tolerate salt well. Large adults sometimes travel more than 1.6 kilometers (1 mile) from water, and in winter they shelter in stumps, burrows and rock crevices on higher ground.
What do cottonmouths eat?
Few snakes in North America eat as wide a variety of prey as the cottonmouth. Fish and frogs make up most of its diet, and it often hunts at the water's edge or waits motionless in the shallows for prey to come within range. It also takes salamanders, birds, small mammals, lizards, small turtles, young alligators and other snakes, including smaller cottonmouths. In Florida, cottonmouths were seen in 2020 and 2021 eating young Burmese pythons, an invasive species in the Everglades. Males and females tend to eat differently: adult males feed mainly on fish, while adult females eat more snakes and lizards. The cottonmouth is also one of the few snakes known to eat carrion regularly. Young cottonmouths have a bright yellow or greenish tail tip that they wiggle like a worm to lure frogs and lizards within reach, a trick called caudal luring. The tail tip turns black as the snake grows, and adults rely instead on ambush or on actively searching the water's edge.
Are cottonmouths aggressive?
The cottonmouth has a reputation for chasing people and attacking boats, but field research tells a different story. In a well known study, researchers approached wild cottonmouths in South Carolina: 23 of 45 snakes tried to escape, and 28 of 36 used threat displays instead of biting. When the researchers simply stood next to them, none bit. Stepped on with a protected boot, fewer than 20 percent tried to bite, and only when picked up with a mechanical hand did about 36 percent attempt it. What makes the cottonmouth seem aggressive is that it often stands its ground instead of fleeing, relying on its warning display: it coils, vibrates its tail, flattens its body, hisses and gapes to show its white mouth. If that is not enough, it releases a strong smelling musk from glands at the base of the tail. Cottonmouths are active by day and by night, and are often found swimming or crawling after dark in warm weather. In the north of their range they spend winter in a state of reduced activity. They also swim very well and can bite underwater.
Baby cottonmouths and reproduction
Cottonmouths do not lay eggs. The eggs develop inside the mother, and the young are born alive in late summer, usually in August or September. A litter usually has 6 to 8 babies, but can range from 1 to 16 and occasionally reach 20. Newborns measure 22 to 35 centimeters and are fully venomous from birth, so a baby cottonmouth deserves the same respect as an adult. They look quite different from their parents: baby cottonmouths are tan, brown or reddish brown with bold dark crossbands, and the tip of the tail is bright yellow or greenish yellow, which they use to lure prey. Because of this pattern they are often mistaken for young copperheads. As they grow, the pattern darkens, and many adults end up almost black. Females can breed before they are three years old if food is plentiful, but they usually have young only every other year. Mothers may stay with their newborns for one to two weeks, until the babies shed their skin for the first time. Cottonmouths are believed to be monogamous, and females have even been shown to produce young without a male, a rare process called facultative parthenogenesis.
Is the cottonmouth venomous? Bite and venom
Yes. The cottonmouth is venomous, and its venom is stronger than the copperhead's. It is mainly cytotoxic: rich in enzymes that destroy tissue and affect the blood, without the nerve attacking toxins found in some rattlesnakes. A bite causes immediate, intense pain, swelling and bruising that can spread up the limb, and in serious cases tissue death that leaves scars or, rarely, leads to amputation. An average bite contains about 125 milligrams of dried venom, and the dose that could kill an adult is estimated at 100 to 150 milligrams, but deaths are very rare. Poison centers in the United States record roughly 225 to 255 cottonmouth bites a year, far fewer than the 2,000 or more from copperheads, and modern records show almost no deaths. Any bite is still a medical emergency. The right response is to move away from the snake, keep calm, remove rings and tight clothing, keep the bitten limb still and get to a hospital, where antivenom such as CroFab works well. Do not cut the wound, suck out venom, apply ice or use a tourniquet. Most bites happen when people try to catch or kill the snake, or step on one hidden in shallow water or bankside vegetation.
Is the cottonmouth endangered?
No. The IUCN lists the cottonmouth as Least Concern, with a stable population trend, because it remains common across most of the southeastern United States. The picture is different at the edges of its range: in Indiana, where only a few populations survive in the far south of the state, it is listed as endangered. The main local threats are the draining of wetlands, the clearing of floodplain forests for farms and towns, and pollution of rivers and swamps that reduces the fish and frogs it eats. Persecution is another serious problem. Many cottonmouths are killed on sight by people who fear them, and the problem is made worse by mistaken identity: harmless water snakes, which are far more common in many places, are killed even more often because people take them for cottonmouths. Its skin has also been used for leather. The cottonmouth plays a useful role in its wetlands as both predator and prey, and in Florida it even eats young invasive Burmese pythons. Protecting swamps, river floodplains and other wetlands across the Southeast is the most important step for its long term survival.
Where it is found
The Cottonmouth Snake can be found in places such as:
