Agkistrodon piscivorus

Common names: cottonmouth, water moccasin, black moccasin, black snake,^[2] more.

Agkistrodon piscivorus is a venomous pitviper species found in the eastern United States. It is a close relative of the copperhead, A. contortrix. Three subspecies are currently recognized, including the nominate subspecies described here.^[3]

Additional recommended knowledge

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Description

This is the largest species of the genus Agkistrodon. Adults commonly exceed 80 cm (roughly 2 ft. 8 in.) in length, with males growing larger than females. They have a heavy body with a moderately long tail. Occasionally, individuals may exceed 180 cm (5.9 ft) in length, especially in the eastern part of the range.^[4]  

The color pattern consists of a brown, gray, tan, yellowish olive or blackish ground color, which is overlaid with a series of 10-17 crossbands that are dark brown to almost black. These crossbands, which usually have black edges, are sometimes broken along the dorsal midline to form a series of staggered half bands on either side of the body. These crossbands are visibly lighter in the center, almost matching the ground color, often contain irregular dark markings, and extend well down onto the ventrals. The dorsal banding pattern fades with ages, so that older individuals are an almost uniform olive brown, grayish brown or black. The belly is white, yellowish white or tan, marked with dark spots, and becomes darker posteriorly. The amount of dark pigment on the belly varies from virtually nothing to almost completely black. The head is a more or less uniform brown color, especially in A. p. piscivorus. Subadult specimens may exhibit the same kind of dark, parietal spots that are characteristic of A. contortrix, but sometimes these are still visible in adults. Eastern populations have broad dark postocular stripe, bordered with pale pigment above and below, that is faint or absent in western populations. The underside of the head is generally whitish, cream or tan.^[4]

Juvenile and subadult specimens generally have a more contrasting color pattern, with dark crossbands on a lighter ground color. The ground color is then tan, brown or reddish brown. The tip of the tail is usually yellowish, becoming greenish yellow or greenish in subadults, and then black in adults. On some juveniles, the banding pattern can also be seen on the tail.^[4]

Common names

Water moccasin, cottonmouth, black moccasin, black snake, blunt-tail moccasin, congo, copperhead, cottonmouth water moccasin, cotton-mouthed snake, gapper, highland moccasin, lowland moccasin, mangrove rattler, moccasin, Florida Cottonmouth^[5], North American cottonmouth snake, North American water moccasin, North American water viper, pilot, rusty moccasin, saltwater rattler, rattler, stub-tail, stump moccasin, stump-tail moccasin, stump-tail viper, swamp lion, Texas moccasin, trap jaw, Troost's moccasin, true horn snake, true water moccasin, viper, water mokeson, water pilot, water rattlesnake, water viper,^[2] cotton-mouth snake.^[6]

Geographic range

Found in the eastern United States from Virginia, south through the Florida peninsula and west to Arkansas, southeastern Kansas, eastern and southern Oklahoma, and eastern and central Texas. A few records exist of the species being found along the Rio Grande in Texas, but these are thought to represent disjunct populations, now possibly extirpated. The type locality given is "Carolina," although Schmidt (1953) proposed that this be restricted to the area around Charleston, South Carolina.^[1]

Campbell and Lamar (2004) mentions this species as being found in Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, eastern Kentucky, Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Texas, and Virginia.^[4] Maps provided by Campbell and Lamar (2004) and Wright and Wright (1957) also indicate its presence in eastern Tennessee and extreme southeastern Nebraska.^[4][2]

In Georgia it is found in the southern half of the state up to a few kilometers north of the fall line with few exceptions. Its range also includes the Ohio River Valley as far north as southern Illinois, and it inhabits many barrier islands off the coasts of the states where it is found.^[4]

Conservation status

This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2001).^[7] Species are listed as such due to their wide distribution, presumed large population, or because it is unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend is stable. Year assessed: 2007.^[8]

It does not hold any other conservation status, and because of its perceived aggressiveness and fear of its bite, many are killed by humans every year. Unfortunately, the far more common species of water snakes of the genus Nerodia are often mistaken for it, and many more of them are killed every year.

Habitat

Cottonmouths are rarely found far from a permanent water source, such as a slow moving stream, edge of a lake, pond, swamp, or even brackish tidal estuaries. Throughout much of their range, they are found in open flatwood pine forests or bald cypress swamps. They are abundant in abandoned rice ditches.

Frequency of encounters

Commonly, the average person will call any snake found in, or near, the water a cottonmouth or water moccasin. This is far from the case. Harmless water snakes (those of the genus Nerodia) are far more common than the cottonmouth, and will sometimes act aggressively and flatten their head to mimic the shape of the pit viper's head. This behavior can be very convincing to people not experienced with these snakes. On land the eastern hognose snake, (Heterodon platirhinos) is also frequently mistaken for the cottonmouth. It too can flatten its head, though not appearing as convincing as the water snake, and will often hiss loudly as a method of defense.

Behavior

Within their range, cottonmouths have a reputation as being aggressive snakes. However, in tests designed to measure the suite of behavioral responses by free-ranging cottonmouths to encounters with humans, 51 percent of the test subjects tried to escape and 78 percent used threat displays or other defensive tactics. Only when the snakes were picked up with a mechanical hand were they likely to bite. ^[9]  

In addition, many of the snakes that did bite did not inject venom. Such a "dry" bite could also be another, more serious threat display. Unlike most snakes, including the copperhead, when startled the cottonmouth often will stand its ground and open its mouth ("gape" or "smile") to warn predators to stay away. That behavior is many times seen as aggressive, but if left alone they will leave.

They take a wide variety of prey including fish, small mammals, lizards, birds, small turtles, baby alligators, and even other snakes. Usually a victim is envenomated quickly with a bite and then released. If the prey does not succumb immediately, it is tracked by scent. Like all pit vipers, the cottonmouth has pits on the sides of its nose that sense bodyheat of warm blooded animals in the form of infrared light, thus its hunting ability is not impaired at night. The name "cottonmouth" is earned by the snake's tendency to open its mouth widely, displaying white tissue inside as a warning gesture.

Reproduction

  A. piscivorus breeds in the spring and fall and is ovoviviparous, giving birth to 10 or so live young after a 3 month gestation period. The young average around 20 cm in length. There is little to no maternal care. Juvenile cottonmouths share a behavior with A. contortrix known as caudal luring. They use the bright color on the tip of their tail as a lure to entice prey items to approach within striking range (a form of aggressive mimicry). As they mature, this tail color fades along with the associated behaviour.

Venom

The venom of the cottonmouth is hemotoxic, causing swelling and necrosis near the site of the wound, and potentially death of the victim if treatment is not received promptly. The venom is more toxic than that of its close cousin the copperhead, but nowhere near as toxic as those of rattlesnakes and other vipers. Treatment generally includes intravenous fluids, antibiotics, and an antivenin like CroFab. Like many vipers, the cottonmouth is capable of inflicting what is referred to as a "dry bite", where no venom is injected, but any bite from a venomous snake should be treated as serious and immediate medical attention sought, even if no immediate effects from the venom are felt. Compared to other venomous snake species in its geographic range the venom of a cottonmouth is relatively weak and is unlikely to kill an otherwise healthy human adult. Antivenin is typically only administered in severe cases, and medical treatment can be necessary to prevent complications. The bite however is extremely painful, prone to gangrene, and loss of digits is possible with subpar treatment.

Subspecies

See also

• List of crotaline species and subspecies
• Crotalinae by common name
• Crotalinae by taxonomic synonyms
• Snakebite

References