Agkistrodon piscivorus

Summary 7

Agkistrodon piscivorus is a venomous snake, a species of pit viper, found in the southeastern United States. Adults are large and capable of delivering a painful and potentially fatal bite. When antagonized, they will stand their ground by coiling their bodies and displaying their fangs. Although their aggression has been exaggerated, on rare occasions territorial males will approach intruders in an aggressive manner. This is the world's only semiaquatic viper, usually found in or near water,...

Taxon biology 8

The cottonmouth, Agkistrodon piscivorus, is a large, venomous snake in the pit viper subfamily (Crotalinae).  This snake is native to the southeastern United States.  The only semi-aquatic viper species, cottonmouths are strong swimmers and most often found in or near water.  Quiet, warm waters such as shallow lakes, streams and marshes make especially attractive habitats.  However, cottonmouths are not restricted to aquatic realms, and inhabit palmetto forest, pine and deciduous woods, prairies and dunes.  They can also swim in brackish and ocean waters, and have crossed large distances to colonized islands off the Gulf and Atlantic coasts of the United States.   

There are three subspecies of cottonmouths.  Agkistrodon piscivorus piscivorus occurs along the Atlantic coast states from the southeastern corner of Virginia (Dismal swamp) into Georgia.  A. p. conanti occurs throughout Florida, and A. p. leucostoma is distributed from Mississippi to eastern Texas, and north through Oklahoma and Arkansas, up the Mississippi river to Indiana, Ohio, West Virginia.   The three subspecies intergrade in Alabama and Georgia. 

Cottonmouths have a large number of common names, including water moccasin, swamp moccasin, gapper, water rattlesnake.  The names cottonmouth and gapper refer to a characteristic defense posture they engage in when disturbed or threatened.  In these situations, the snake winds itself into an “S” shape, puts its head back with jaws wide to reveal the bright white insides of its mouth, and hisses.  Another defensive strategy they engage in is spraying thin jets of pungent secretions from glands at the base of their tail.  While cottonmouths have a reputation as being aggressive, research finds that they are secretive and usually act defensively when threatened, biting only if caught.  Their bite, however, is extremely painful and potentially (though rarely) fatal to humans.  The venom is a cytotoxin that destroys tissue, but does not cause a whole system reaction.  Bites can be effectively treated with CroFab antivenom, which is derived from venoms of all four known Agkistrodon species.

Adult cottonmouths have large heads, usually brown or olive in color.  Their brown bodies have darker brown crossbands, and their tail is black.  Adults reach up to 1.8 meters (6 feet) long, with males generally larger than females.  Adult cottonmouths have few predators, and can live up to 24.5 years.

Cottonmouths are monogamous and breed usually between April-May.  Females hold the eggs inside their body to develop for 5 months, then give birth to live young (called ovoviparous).  An average clutch numbers 5-9 offspring.  Mothers leave the young after a few days. Raccoons, dogs, cats, birds of prey, egrets, snapping turtles and predatory fish are among the predators of young cottonmouths.  There is a high predation rate, and it is estimated that only 2-3 young per clutch survive. Juveniles are similar in patterning to adults but lighter in coloring so banding stands out more.  Young snakes have yellow markings on their tails, which they sometimes use to lure prey into striking distance.  As they age their coloration gets darker.

Cottonmouths are most active by night, but are also out in daylight hours, often basking.  Further north, they hibernate in the winter.  Their diet is described as omni-carnivorous - basically, they will eat anything they can catch.  This includes any kind of vertebrate (mammals, fish, amphibians, reptiles including other cottonmouths, birds), insects and other invertebrates.  Cottonmouths incapacitate their prey by biting and injecting them with their strong venom.  In addition to live food, cottonmouths also eat carrion. 

One example of extreme diet specialization in cottonmouths occurs in a large population inhabiting the island of Seahorse Key, off the coast of Florida.  There they scavenge on fish carrion provided in the form of vomit, excrement, and dropped fish pieces by resident birds.  In this unusual case, researchers hypothesize the bird-snake interaction is a mutualism.  The birds feed the snakes easy to eat, predigested fish and in return benefit from the snakes minimizing the presence of their biggest predator: rats.  Researchers find no evidence that snakes eat the birds on Seahorse Key.  Both birds and snakes live in larger numbers when on the same island than either do when without each other.

(de Pastino, 2007; Lillywhite and McCleary 2008; Means 2004; Hammerson 2007; Wikipedia 2016)

Sources and Credits

  1. (c) tom spinker, some rights reserved (CC BY-NC-ND),
  2. John Willson at the Savannah River Ecology Laboratory (SREL), no known copyright restrictions (public domain),
  3. (c) Andy Jones, some rights reserved (CC BY-NC-SA),
  4. (c) Mark Pyle, some rights reserved (CC BY-NC),
  5. (c) Valerie Sadler, some rights reserved (CC BY-NC),
  6. (c) Valerie Sadler, some rights reserved (CC BY-NC),
  7. (c) Wikipedia, some rights reserved (CC BY-SA),
  8. (c) Dana Campbell, some rights reserved (CC BY-SA),

More Info