Cottonmouth Snake

''Agkistrodon piscivorus'' is a species of venomous snake, a pit viper in the subfamily Crotalinae of the family Viperidae. It is one of the world's few semiaquatic vipers (along with the Florida cottonmouth), and is native to the Southeastern United States. As an adult, it is large and capable of delivering a painful and potentially fatal bite. When threatened, it may respond by coiling its body and displaying its fangs. Individuals may bite when feeling threatened or being handled in any way. It tends to be found in or near water, particularly in slow-moving and shallow lakes, streams, and marshes. It is a capable swimmer, and like several species of snakes, is known to occasionally enter bays and estuaries and swim between barrier islands and the mainland. 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. .

The generic name is derived from the Greek words ' "fish-hook, hook" and "tooth", and the specific name comes from the Latin 'fish' and '(I) eat greedily, devour'; thus, the scientific name translates to "hook-toothed fish-eater". Common names include cottonmouth, northern cottonmouth, water moccasin, swamp moccasin, black moccasin, and simply viper. Wright AH, Wright AA (1957). '' Handbook of Snakes of the United States and Canada''. Ithaca and London: Comstock Publishing Associates, a Division of Cornell University Press. (7th printing, 1985). 1,105 pp. (in 2 volumes) . (''Ancistrodon piscivorus'', pp. 916–925, Figures 263–265, Map 65). Many of the common names refer to the threat display, in which this species often stands its ground and gapes at an intruder, exposing the white lining of its mouth. Many scientists dislike the use of the term water moccasin since it can lead to confusion between the venomous cottonmouth and nonvenomous water snakes.

Taxonomy and etymology

Common names

This is a list of common names for ''A. piscivorus'', some of which also refer to other species:

*aquatic moccasin
*black moccasin
*black snake
*black water viper
*blunt-tail moccasin
*Congo
*copperhead
*cottonmouth
*cotton-mouthed snake
*cottonmouth rattler
*cottonmouth water moccasin
*gape
USGS
*gapper
*highland moccasin
*lake moccasin
*lowland moccasin
*mangrove rattler
*moccasin
*moccasin snake
*North American cottonmouth snake
*North American water moccasin
*North American water viper
*pond moccasin
*pond rattler
*river moccasin
*river rattler
*rusty moccasin
*saltwater rattler
*short-tailed moccasin
*short-tail rattler
*small-tailed cottonmouth
*snap-jaw
*stub-tail
*stub-tail snake
*stump moccasin
*stump-tail moccasin
*stump-tail viper
*swamp lion
*swamp moccasin
*swamp rattler
*Texas moccasin
*trap jaw
* Troost's moccasin
*true horn snake
*true water moccasin
*viper
*water copperhead
*water mamba
*water moccasin
*water mokeson
*water pilot
*water pit rattler
*water pit viper
*water rattlesnake
*water viper
*white-mouth moccasin
*white-mouth rattler
*worm-tailed viper

Subspecies and taxonomic history

For many decades, one species with three subspecies were formally recognized: eastern cottonmouth, ''A. p. piscivorus'' ( Lacépède, 1789); Lacepède BGE (1789). ''Histoire Naturelle des Quadrupèdes Ovipares et de Serpens. Vol.2.'' Paris: lmprimerie du Roi. 671 pp. western cottonmouth, ''A. p. leucostoma'' ( Troost, 1836); Troost, Gerardus (1836). "On a new genus of serpents, and two new species of the genus ''Heterodon'', inhabiting Tennessee". ''Annals of the Lyceum of Natural History of New York'' 3: 174–190. and Florida cottonmouth, ''A. p. conanti'' Gloyd, 1969.Gloyd, Howard K. (1969). "Two additional subspecies of North American crotalid snakes, genus ''Agkistrodon'' ". ''Proceedings of the Biological Society of Washington'' 82: 219–232. However, a molecular (DNA) based study was published in 2014, applying phylogenetic theories (one implication being no subspecies are recognized), changing the long-standing taxonomy. The resulting and current taxonomic arrangement recognizes two species and no subspecies. The western cottonmouth (''A. p. leucostoma'') was synonymized with the eastern cottonmouth (''A. p. piscivorus'') into one species (with the oldest published name, ''A. p. piscivorus'', having priority). The Florida cottonmouth (''A. p. conanti'') is now recognized as a separate species. Burbrink, Frank T.; Guiher, Timothy J. (2014)
"Considering gene flow when using coalescent methods to delimit lineages of North American pitvipers of the genus ''Agkistrodon'' ".
''Zoological Journal of the Linnean Society'' 173: 505–526.

* ''Agkistrodon piscivorus'' (Lacépéde, 1789), northern cottonmouth Crother, Brian I. (editor) (2017). ''Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico, with Comments Regarding Confidence in Our Understanding.'' SSAR (Society for the Study of Amphibians and Reptiles) Herpetological Circular 43. 102 pp. (p. 59)
* ''Agkistrodon conanti'' Gloyd, 1969, Florida cottonmouth (south Georgia and Florida peninsula)

Anatomy and description

''Agkistrodon piscivorus'' is the largest species of the genus ''Agkistrodon''. Adults commonly exceed in total length (including tail); females are typically smaller than males. Total length, per one study of adults, was . Average body mass has been found to be in males and in females. Occasionally, individuals may exceed in total length, especially in the eastern part of the range.Campbell JA, Lamar WW (2004). ''The Venomous Reptiles of the Western Hemisphere''. Ithaca and London: Comstock Publishing Associates. 870 pp. 1,500 plates. .

Although larger ones have purportedly been seen in the wild, according to Gloyd and Conant (1990), the largest recorded specimen of ''A. p. piscivorus'' was in total length, based on a specimen caught in the Dismal Swamp region and given to the Philadelphia Zoological Garden. This snake had apparently been injured during capture, died several days later, and was measured when straight and relaxed. Large specimens can be extremely bulky, with the mass of a specimen of about in total length known to weigh .

Many would assume that the morphology of an aquatic snake should have a small, narrow head that tapers towards the back to minimize drag in the water, especially when capturing prey. However, the pit vipers, and particularly cottonmouths, display a contradicting structure, with its bulky, triangular head, which would be assumed to be poorly suited to water, yet it is not the case.

The broad head is distinct from the neck, and the snout is blunt in profile with the rim of the top of the head extending forwards slightly further than the mouth. Substantial cranial plates are present, although the parietal plates are often fragmented, especially towards the rear. A loreal scale is absent. Six to 9 supralabials and eight to 12 infralabials are seen. At midbody, it has 23–27 rows of dorsal scales. All dorsal scale rows have keels, although those on the lowermost scale rows are weak. In males/females, the ventral scales number 130-145/128-144 and the subcaudals 38-54/36-50. Many of the latter may be divided.

Though most specimens are almost or even totally black, (with the exception of the head and facial markings), the color pattern may consist of a brown, gray, tan, yellowish-olive, or blackish ground color, which is overlaid with a series of 10–17 dark brown to almost black crossbands. These crossbands, which usually have black edges, are sometimes broken along the dorsal midline to form a series of staggered halfbands 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 ventral scales. The dorsal banding pattern fades with age, so 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 none 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 characteristic of '' A. contortrix'', but sometimes these are still visible in adults. Eastern populations have a 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. Specimens between 26.8 cm and 120.3 cm snout-vent lengths displayed various dorsal colors (including white, tan, brown, and black). Those greater than 60 cm snout-vent length had less white and tan colors.

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. Young snakes wiggle the tips of their tails to lure prey animals.

This species is often confused with the copperhead, '' A. contortrix''. This is especially true for juveniles, but differences exist. ''A. piscivorus'' has broad, dark stripes on the sides of its head that extend back from the eyes, whereas ''A. contortrix'' has only a thin, dark line that divides the pale supralabials from the somewhat darker color of the head. The watersnakes of the genus ''Nerodia'' are also similar in appearance, being thick-bodied with large heads, but they have round pupils, no loreal pit, a single anal plate, subcaudal scales that are divided throughout, and a distinctive overall color pattern.

Venom

''Agkistrodon piscivorus'' venom is more toxic than that of ''A. contortrix'', and is rich with powerful cytotoxic venom that destroys tissue. Although deaths are rare, the bite can leave scars, and on occasion, require amputation. Absent an anaphylactic reaction in a bitten individual, however, the venom does not cause systemic reactions in victims and does not contain neurotoxic components present in numerous rattlesnake species. Bites can be effectively treated with CroFab antivenom; this serum is derived using venom components from four species of American pit vipers (the eastern and western diamondback rattlesnakes, the Mojave rattlesnake, and the cottonmouth).''Agkistrodon piscivorus''
a
Munich AntiVenom INdex (MAVIN)
Accessed 18 June 2008.

Bites from the cottonmouth are relatively frequent in the lower Mississippi River Valley and along the coast of the Gulf of Mexico, although fatalities are rare. Allen and Swindell (1948) compiled a record of ''A. piscivorus'' bites in Florida from newspaper accounts and data from the Bureau of Vital Statistics: 1934, eight bites and three fatalities (no further fatalities were recorded after this year); 1935, 10; 1936, 16; 1937, 7; 1938, 6; 1939, 5; 1940, 3; 1941, 6; 1942, 3; 1943, 1; 1944, 3; 1998, 1. Wright and Wright (1957) report having encountered these snakes on countless occasions, often almost stepping on them, but never being bitten. In addition, they heard of no reports of any bites among 400 cypress cutters in the Okefenokee Swamp during the entire summer of 1921. These accounts suggest that the species is not particularly aggressive. Studies show that stressed snakes are more likely to strike. This action comes as a predator defense mechanism. Snakes with elevated hormone levels are more likely to strike. Additionally, larger snakes are more likely to strike than smaller snakes.

Brown (1973) gave an average venom yield (dried) of 125 mg, with a range of 80–237 mg, along with values of 4.0, 2.2, 2.7, 3.5, 2.0 mg/kg IV, 4.8, 5.1, 4.0, 5.5, 3.8, 6.8 mg/kg IP and 25.8 mg/kg SC for toxicity. Wolff and Githens (1939) described a specimen that yielded 3.5 ml of venom during the first extraction and 4.0 ml five weeks later (1.094 grams of dried venom). The human lethal dose is unknown, but has been estimated at 100–150 mg.

Symptoms commonly include ecchymosis and swelling. The pain is generally more severe than bites from the copperhead, but less so than those from rattlesnakes ( ''Crotalus'' spp.). The formation of vesicles and bullae is less common than with rattlesnake bites, although necrosis can occur. Myokymia is sometimes reported.Norris R (2004). "Venom Poisoning in North American Reptiles". ''In'': Campbell JA, Lamar WW (2004). ''The Venomous Reptiles of the Western Hemisphere.'' Ithaca and London: Comstock Publishing Associates. 870 pp. 1,500 plates. . However, the venom has strong proteolytic activity that can lead to severe tissue destruction.

Geographic range

''A. piscivorus'' is found in the eastern US from the Great Dismal Swamp in southeast Virginia, south through the Florida peninsula and west to Arkansas, eastern and southern Oklahoma, and western and southern Georgia (excluding Lake Lanier and Lake Allatoona). 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 eradicated. The type locality given is "Carolina", although Schmidt (1953) proposed this be restricted to the area around Charleston, South Carolina. McDiarmid RW, Campbell JA, Touré TA (1999). ''Snake Species of the World: A Taxonomic and Geographic Reference, Volume 1.'' Washington, District of Columbia: Herpetologists' League. 511 pp. (series). (volume). Snakes observed in the northern areas of this range are typically larger older individuals.

Campbell and Lamar (2004) mentioned this species as being found in Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, and Virginia. Maps provided by Campbell and Lamar (2004) and Wright and Wright (1957) also indicate its presence in Western and Middle Tennessee and extreme southeastern Kansas, and limit it to the western part of Kentucky.

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 Indiana, and it inhabits many barrier islands off the coasts of the states where it is found.

Habitat

''Agkistrodon piscivorus'' 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. This species has a unique swimming pattern and appears to be floating on top of the water rather than swimming with its body beneath the surface. The U.S. Navy (1991) describes it as inhabiting swamps, shallow lakes, and sluggish streams, but it is usually not found in swift, deep, cool water.U.S. Navy (1991). ''Poisonous Snakes of the World''. New York: United States Government / Dover Publications, Inc. 203 pp. . 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. Behler JL, King FW (1979). ''The Audubon Society Field Guide to North American Reptiles and Amphibians.'' New York: Alfred A. Knopf. 743 pp. 657 plates. LCCCN 79-2217. . (''Agkistrodon piscivorus'', pp. 684-685 + Plates 654, 656, 657).

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. Even on these islands, though, it tends to favor freshwater marshes. A study by Dunson and Freda (1985) describes it as not being particularly salt-tolerant.

The snake is not limited to aquatic habitats, however, as Gloyd and Conant (1990) mentioned large specimens have been found more than a mile (1.6 km) from water. In various locations, the species is well-adapted to less moist environments, such as palmetto thickets, pine-palmetto forest, pine woods in East Texas, pine flatwoods in Florida, eastern deciduous dune forest, dune and beach areas, riparian forest, and prairies.

Behavior and ecology

In the United States, especially in the south, ''A. piscivorus'' are often falsely characterized as aggressive. In tests designed to measure the various behavioral responses by wild specimens to encounters with people, 23 of 45 (51%) tried to escape, while 28 of 36 (78%) resorted to threat displays and other defensive tactics. Only when they were picked up with a mechanical hand were they likely to bite. Gibbons JW, Dorcas ME (2002). "Defensive Behavior of Cottonmouths (''Agkistrodon piscivorus'') toward Humans". SREL Reprint #2583
Summary
at th
Savannah River Ecology Laboratory
at th
University of Georgia
Accessed May 29, 2007. 36% of those picked up attempted to bite. Furthermore, less than 20% attempted to bite when stepped on. None of the snakes attempted to bite when researchers stood next to them.

When approached by humans, cottonmouths seek the closest shelter possible. At times this means moving closer to humans, giving the impression that it is seeking to harm them. This behavior is often seen in conjunction with a raising of the head, leading to further misinterpretations.

When sufficiently stressed or threatened, this species engages in a characteristic threat display that includes vibrating its tail and throwing its head back with its mouth open to display the startlingly white interior, often making a loud hiss while the neck and front part of the body are pulled into an S-shaped position. Carpenter, Charles C.; Gillingham, James C. (1990). "Ritualized Behavior in ''Agkistrodon'' and Allied Genera". pp. 523–531. ''In'': 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. . Many of its common names, including "cottonmouth" and "gaper", refer to this behavior, while its habit of snapping its jaws shut when anything touches its mouth has earned it the name "trap jaw" in some areas.Conant R, Bridges W (1942). ''What Snake Is That? A Field Guide to the Snakes of the United States East of the Rocky Mountains.'' (With 108 drawings by Edmond Malnate). New York and London: D. Appleton-Century Company. Frontispiece map + viii + 163 pp. + Plates A–C, 1–32. (''Agkistrodon piscivorus'' pp. 140–141 + Plate 28, Figure 82). Other defensive responses can include flattening the body and emitting a strong, pungent secretion from the anal glands located at the base of the tail. This musk may be ejected in thin jets if the snake is sufficiently agitated or restrained. The smell has been likened to that of a billy goat, as well as to a genus of common flood-plain weeds, ''Pluchea'', that also have a penetrating odor.

Harmless watersnakes of the genus ''Nerodia'' are often mistaken for it. These are also semiaquatic, thick-bodied snakes with large heads that can be aggressive when provoked, but they behave differently. For example, watersnakes usually flee quickly into the water, while ''A. piscivorus'' often stands its ground with its threat display. In addition, watersnakes do not vibrate their tails when excited.Conant R (1975). ''A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Second Edition.'' First published in 1958. Boston: Houghton Mifflin Company. xviii + 429 pp. + 48 plates. (hardcover), (paperback). (''Agkistrodon piscivorus'', pp. 228–230 + Plate 34 + Map 173). ''A. piscivorus'' usually holds its head at an angle around 45° when swimming or crawling.

Brown (1973) considered their heavy muscular bodies to be a striking characteristic, stating this made it difficult to hold them for venom extraction owing to their strength.Brown, John Haynes (1973). ''Toxicology and Pharmacology of Venoms from Poisonous Snakes''. Springfield, Illinois: Charles C. Thomas. 184 pp. LCCCN 73-229. .

This species may be active during the day and at night, but on bright, sunny days, they are usually found coiled or stretched out in the shade. In the morning and on cool days, they can often be seen basking in the sunlight. They often emerge at sunset to warm themselves on warm ground (i.e., sidewalks, roads) and then become very active throughout the night, when they are usually found swimming or crawling. Contrary to popular belief, they are capable of biting while under water.

A number of parasites are known to inhabit the species. Examples of parasitic species include ''K. coarctatus'' and ''P. ctotali''. The parasites are known to cause infection of the lungs, but not inflammation.

In the north, they hibernate during the winter. Niell (1947, 1948) made observations in Georgia, and noted they were one of the last species to seek shelter, often being found active until the first heavy frosts. At this point, they moved to higher ground and could be found in rotting pine stumps by tearing away the bark. These snakes could be quite active upon discovery and would then attempt to burrow more deeply into the soft wood or escape to the nearest water. In southeastern Virginia, Wood (1954) reported seeing migratory behavior in late October and early November. During a period of three or four days, as many as 50 individuals could be seen swimming across Back Bay from the bayside swamps of the barrier islands to the mainland. He suggested this might have something to do with hibernating habits. In the southern parts of its range, hibernation may be short or omitted altogether.

Hunting and diet

Raymond Ditmars (1912) described ''A. piscivorus'' as carnivorous. Its diet includes mammals, birds, amphibians, fish, eggs, insects, other 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. Catfish (especially of the genus ''Ictalurus'') are often eaten, although the sharp spines sometimes cause injuries. Toads of the genus ''Bufo'' are apparently avoided. Common prey species include southern leopard frogs, bass, juvenile black rat snake