Agkistrodon piscivorus
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| Agkistrodon piscivorus (Lacépède, 1789) |
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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]
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[edit] 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] According to Gloyd and Conant (1990), the largest recorded specimen of A. p. piscivorus was 74 inches (1879 mm) in length (Conant, 1975), based on a specimen caught in the Dismal Swamp region and given to the Philadelphia Zoological Garden. It should be noted, however, that this snake had apparently been injured during capture, died several days later and was measured when straight and relaxed.[5]
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]
[edit] 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, 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]
[edit] 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, 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, extreme southeastern Nebraska and limit it to the western part of Kentucky.[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]
[edit] 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.
[edit] Habitat
This is the most aquatic species of the genus Agkistrodon and is usually associated with bodies of water, such as creeks, streams, marshes, swamps and the shores of ponds and lakes.[4] The U.S. Navy (1991) describes it as inhabiting swamps, shallow lakes and sluggish streams, but that it is usually not found in swift, deep, cool water.[9] Behler and King (1979) list its habitats as including lowland swamps, lakes, rivers, bayheads, sloughs, irrigation ditches, canals, rice fields and small clear rocky mountain streams.[10]
It is also found in brackish water habitats and is sometimes seen swimming in salt water. It has been much more successful at colonizing Atlantic and Gulf coast barrier islands than the copperhead, A. contortrix. However, even on these islands it tends to favor freshwater marshes. A study by Dunson and Freda (1985) describes it as not being particularly salt tolerant.[4]
Not limited to water, however, Gloyd and Conant (1990) mention that large specimens have been found more than a mile (1.6 km) from any visible sources of it.[5] In various locations the species is well adapted to less moist environments, such as palmetto thickets, pine-palmetto forest, pine woods in eastern Texas, pine flatwoods in Florida, eastern deciduous dune forest, dune and beach areas, riparian forest and prairies.[4]
[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] 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.[11]
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 are semi-aquatic, spending almost all their time close to permanent water sources. They swim with much of their bodies floating above the surface distinguishing them from water snakes, which tend to swim mostly below the surface, sometimes with their heads protruding.
The name "cottonmouth" is earned by the snake's tendency to open its mouth widely, displaying white tissue inside as a warning gesture.
[edit] Feeding
Ditmars (1912) described this species as omnicarnivorous. Its diet includes mammals, birds, amphibians, fish, snakes, small turtles and small alligators. Cannibalism has also been reported. Normally, though, the bulk of its diet consists of fish and frogs. On occasion, juvenile specimens feed on invertebrates.[5] Catfish are often eaten, although the sharp spines sometimes cause injuries. Toads of the genus Bufo are apparently avoided.[4]
Many authors have described the prey items taken under natural circumstances. Although fish and frogs are their most common prey, they will eat almost any small vertebrate. Campbell and Lamar (2004) provide an exhaustive list of species that have reportedly been preyed upon by A. piscivorus, including cicadas, caterpillars, land snails (Euglandina rosea), catfish (Ictalurus furcatus), pike (Esox ssp.), sunfishes (Lepomis ssp.), bass (Micropterus ssp.), sirens (Siren sp.), eastern newts (Notophthalmus viridescens), brook salamanders (Eurycea sp.), Ouachita dusky salamanders (Desmognatus brimleyorum), spadefoot toads (Scaphiopus), eastern narrowmouth toads (Gastrophryne carolinensis), northern cricket frogs (Acris crepitans), West Indian treefrogs (Osteopilus septentrionalis), treefrogs (Hyla sp.), true frogs (Rana sp.), green anoles (Anolis carolinensis), skinks (Eumeces sp.), eastern glass lizards (Ophisaurus ventralis), ground skinks (Scincella lateralis), mudsnakes (Farancia abacura), hog-nosed snakes (Heterodon platirhinos), kingsnakes (Lampropeltis sp.), watersnakes (Nerodia sp.), crayfish snakes (Regina sp.), brown snakes (Storeria dekayi), gartersnakes and ribbonsnakes (Thamnophis sp.), other cottonmouths (A. piscivorus), rattlesnakes (Crotalus sp.), common snapping turtles (Chelydra serpentina), mud turtles (Kinosternon sp.), common musk turtles (Sternotherus odoratus), Florida cooters (Pseudemys floridana), sliders (Trachemys scripta), eastern box turtles (Terrapene carolina), Florida softshell turtles (Apalone ferox), baby American alligators (Alligator mississippiensis), wood thrushes (Hylocichla mustelina), chickadees (Parus sp.), cardinals (Cardinalis cardinalis), unidentified passerines, small ducks, juvenile anhingas (Anhinga anhinga), common egrets (Ardea alba), egrets, glossy ibises and their eggs (Plegadis falcinellus), tricolor herons (Egretta tricolor), herons and their eggs, pied-billed grebes (Podilymbus podiceps), short-tailed shrews (Blarina brevicauda), least shrews (Cryptotis parva), southeastern shrews (Sorex longirostris), eastern moles (Scalopus aquaticus), muskrats (Ondatra zibethicus), rice rats (Oryzomys palustris), hispid pocket mice (Perognathus hispidus), black rats (Rattus rattus), squirrels (Sciurus sp.), rabbits (Sylvilagus sp.) and bats.[4]
They are opportunistic feeders and will sometimes eat carrion. Campbell and Lamar (2004) describe having seen them feeding on fish heads and viscera that had been thrown into the water from a dock. Heinrich and Studenroth (1996) report an occasion in which an individual was seen feeding on the butchered remains of a wild hog (Sus scrofa) that had been thrown into Cypress Creek.[4]
Conant (1929) gives a detailed account of the feeding behavior of a captive specimen from South Carolina. When prey was introduced, the snake quickly became attentive and made an attack. Frogs and small birds were seized and held until movement stopped. Larger prey was approached in a more cautious manner; a rapid strike was executed after which the snake would withdraw. In 2.5 years the snake had accepted three species of frogs, including a large bullfrog, a spotted salamander, water snakes, garter snakes, sparrows, young rats and three species of mice.[5]
Brimley (1944) described a captive specimen that ate copperheads (Agkistrodon contortrix), as well as members of its own species, keeping its fangs embedded in its victims until they had been immobilized.[5]
[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 (a form of aggressive mimicry). As they mature, this tail color fades along with the associated behaviour.
[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 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.
[edit] Subspecies
| Subspecies[3] | Authority[3] | Common name[5] | Geographic range[5] |
|---|---|---|---|
| A. p. conanti | Gloyd, 1969 | Florida cottonmouth | The United States, in extreme southern Georgia and virtually all of the state of Florida, including many of the islands off the coast. |
| A. p. leucostoma | (Troost, 1836) | Western cottonmouth | The United States, from southern Alabama along coast of the Gulf of Mexico, including many offshore islands, to southeastern and central Texas, and north to Oklahoma, Missouri, Illinois and Indiana. |
| A. p. piscivorus | (Lacépède, 1789) | Eastern cottonmouth | The United States in southeastern Virginia, the Atlantic Coastal Plain and lower Piedmont of North and South Carolina, including the banks, peninsulas and islands along the Atlantic coast, and west across Georgia. |
[edit] See also
- List of crotaline species and subspecies
- Crotalinae by common name
- Crotalinae by taxonomic synonyms
- Snakebite
[edit] References
- ^ a b McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. ISBN 1-893777-00-6 (series). ISBN 1-893777-01-4 (volume).
- ^ a b c Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates. (7th printing, 1985). 1105 pp. ISBN 0-8014-0463-0.
- ^ a b c Agkistrodon piscivorus (TSN 174299). Integrated Taxonomic Information System. Retrieved on 29 May 2007.
- ^ a b c d e f g h i j k l Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.
- ^ a b c d e f g Gloyd HK, Conant R. 1990. Snakes of the Agkistrodon Complex: A Monographic Review. Society for the Study of Amphibians and Reptiles. 614 pp. 52 plates. LCCN 89-50342. ISBN 0-916984-20-6.
- ^ Ditmars RL. 1933. Reptiles of the World. Revised Edition. The MacMillan Company. 329 pp. 89 plates.
- ^ Agkistrodon piscivorus at the IUCN Red List. Accessed 13 September 2007.
- ^ 2001 Categories & Criteria (version 3.1) at the IUCN Red List. Accessed 13 September 2007.
- ^ U.S. Navy. 1991. Poisonous Snakes of the World. US Govt. New York: Dover Publications Inc. 203 pp. ISBN 0-486-26629-X.
- ^ Behler JL, King FW. 1979. The Audubon Society Field Guide to North American Reptiles and Amphibians. New York: Alfred A. Knopf. 743 pp. LCCCN 79-2217. ISBN 0-394-50824-6.
- ^ Whitfield Gibbons J, Dorcas ME. 2002. Defensive Behavior of Cottonmouths (Agkistrodon piscivorus) toward Humans. SREL Reprint #2583. Summary at the Savannah River Ecology Laboratory at the University of Georgia. Accessed May 29, 2007.
[edit] External links
- Agkistrodon piscivorus at the TIGR Reptile Database. Accessed 7 December 2007.
- Cottonmouth close up photos at rlephoto.com. Accessed 7 December 2007.
- Cottonmouth Fact Sheet at Smithsonian National Zoological Park. Accessed 7 December 2007.
