Agkistrodon piscivorus
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 Cottonmouth, Agkistrodon piscivorus
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| Agkistrodon piscivorus Lacépède, 1789 |
Agkistrodon piscivorus is a pit viper species found in the United States. Commonly called cottonmouth or water moccasin, it is a close relative of the copperhead (A. contortrix). There are three recognized subspecies of cottonmouths.
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[edit] Description
A. piscivorus varies greatly in size, with A. p. conanti being the largest. They average between 20 and 48 inches (51 to 121 cm) in length, with the largest recorded length at 74.5 inches (189 cm).[1] They are typically dark in color, either black, dark brown, or a dark olive green, with a muddy appearance. Sometimes muted banding is present. Juveniles have a more striking appearance, with distinctive light and dark banding and a bright yellow-green tail tip. As they age, the banding and color on the tail tip fade.
[edit] 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.
[edit] Behaviour
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. [1] 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.
These snakes, though heavy bodied, are capable of climbing low branches, and will sometimes be seen sunning themselves on branches overhanging water. They are a semi-aquatic species, spending almost all their time in or very close to permanent water sources. They swim with their entire body skimming along the surface; this distinguishes them from water snakes, which tend to swim below the surface.
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 it 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.
[edit] 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. As they mature, this tail color fades along with the associated behavior.
[edit] Range and habitat
A. p. piscivorus is found along the eastern coast of the United States from Virginia to Alabama. A. p. leucostoma is found as far west as central Texas, through eastern Oklahoma, Missouri, as far north as southern Illinois, and east to Kentucky, Tennessee and Alabama. A. p. conanti is found in the state of Florida and southern Georgia. Their ranges overlap, and intergrading of subspecies is not known.
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.
[edit] 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 its close cousin the copperhead, but nowhere near as toxic as 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.
[edit] Subspecies
| Subspecies | Authority | Common name | Geographic range |
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| A. p. conanti | Gloyd, 1969 | Florida cottonmouth | United States (Florida and southern Georgia) |
| A. p. leucostoma | Troost, 1836 | Western cottonmouth | United States (from the Mexican border in Texas through east Oklahoma to central Missouri and southern Illinois, western Kentucky, Tennessee to Mobile Bay, Alabama) |
| A. p. piscivorus | Lacépède, 1789 | Eastern cottonmouth | United States (Atlantic coastal plain south from south-east Virginia west to Alabama) |
[edit] Conservation status
The cottonmouth does not hold any particular conservation status, but 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 cottonmouths and many more of them are killed every year than cottonmouths.
