Cottonmouth (Agkistrodon piscivorus)

Also known as: water moccasin
GenusAgkistrodon (1)
SizeAdult length: 61 - 182 cm (2) (3)
Juvenile length: 20 - 33 cm (3)
Top facts

The cottonmouth is classified as Least Concern (LC) on the IUCN Red List (1).

The cottonmouth (Agkistrodon piscivorus) is North America’s only venomous aquatic snake (3). It gets its common name from the inner white lining of the mouth, which is displayed during this species’ characteristic defensive gaping behaviour (4). The scientific name of this species is also rather descriptive, as the genus name Agkistrodon means ‘fish hook tooth’, while piscivorus means ‘fish eater’ (5). There are three subspecies of cottonmouth, which differ in range and skin pattern (6).

As is typical of vipers, the cottonmouth has a broad, triangular-shaped head which is much wider than its neck (5) (6). Heat-sensing pits, which help to detect warm-blooded prey, are located on the front of the face between the nostrils and the eyes (3). The eyes of the cottonmouth, which have vertically-slit, elliptical-shaped pupils, are invisible from above and are protected by a broad ridge of plate-like scales (7).

The scales of the cottonmouth have a ridge running down the centre, giving them a rough texture. These are known as ‘keeled scales’, and are patterned with a wide, dark, olive-brown cross on a brown or yellowish base colour (2). Colouration can be highly variable in this species, and the patterns on mature cottonmouths often become obscured, resulting in an almost totally solid dark brown to black appearance (7). The underbelly is paler and has yellow-brown blotches (8).

Juvenile cottonmouths are more brightly coloured with very distinctive markings. The body has a brown base colour with red-brown, hourglass-shaped bands, and the tip of the tail is sulphur-yellow (3). The cottonmouth uses this as a lure to attract prey by wiggling it around, simulating a worm (7).

The cottonmouth is endemic to the United States and is found abundantly within the south-eastern states. It ranges south from the Florida Peninsula and south-eastern Virginia, west to central and eastern Texas, Oklahoma, Arkansas, Missouri and south-eastern Kansas, and north to southern Illinois (1). Although usually found on the mainland, populations of the cottonmouth have also been observed on offshore islands (9).

The cottonmouth is a ground-dwelling, semi-aquatic snake (10), and may be found in a variety of habitats (11). These include riparian zones around streams, river floodplains, swamps, wetlands and marshes (2). It may also be found in drainage ditches (3), as well as in ponds and streams within pine forest and offshore keys (1). The cottonmouth is usually found close to water and occurs up to elevations of 700 metres (12).

In the cooler parts of its range, the cottonmouth hibernates and therefore requires different habitat depending on the time of year. Generally, dry upland areas are selected for hibernation and wet lowland areas are used for summer foraging (13).

Is has been suggested that the cottonmouth is North America’s most aggressive snake (14) because it frequently stands its ground if threatened (3). When threatened, this species first tries to escape before using defensive behaviour such as mouth gaping, tail vibrations, odour-release and, eventually, striking and biting (15). It is thought that tail vibrations are used to mimic the warning behaviour of the closely related rattlesnake (14).

The cottonmouth is active during the day or at night, and in much of its range it can be seen all year round (2), except in cooler areas where it hibernates (13).

This well-camouflaged, highly venomous ambush predator generally forages at night when temperatures are cooler (16). Coiling into a ‘strike’ position, it waits for prey to pass, before biting and releasing its victim. The cottonmouth then follows the scent of its stricken prey, waiting for it to die before swallowing it head first (3). Cottonmouth venom causes tissue damage, kidney failure and cardiac arrest in its victims due to the fast-acting enzymes and proteins (17).

An opportunistic, generalist feeder (18), the cottonmouth eats fish, arthropods, reptiles, amphibians and mammals. Like other snakes, prey selection of cottonmouths is limited by the size of its mouth, resulting in a difference in diets between adults and juveniles (19).

Large adult cottonmouths have few predators, although snapping turtles, alligators, large wading birds and owls may feed on them (3). Adult cottonmouths are cannibalistic and are known to eat juveniles (13) (18).

In late August to September, the female cottonmouth gives birth to six to eight live young, which are fully-formed and full of venom (3).

Human activity is the main threat to the cottonmouth, as this species often lives in human-influenced environments where it suffers from persecution and habitat loss (20). The United States has lost an estimated 53 percent of its wetlands over the last 200 years, but active wetland conservation is now taking place (21).

Due to assumed healthy population numbers, there is no known conservation action targeting the cottonmouth.

However, some areas of its habitat, such as the Florida Everglades, are protected under national legislation including The Wilderness Act 1964 (22), the Endangered Animals Act and the Clean Water Act, 1972 (23). The Everglades National Park is also protected by international agreements and is a United Nations Educational, Scientific and Cultural Organisation (UNESCO) World Heritage Site, an International Biosphere Reserve (24) (25), and a Ramsar Convention Wetland of International Importance (25) (26).

Learn more about reptile conservation:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. IUCN Red List (February, 2010)
  2. Savannah River Ecology Laboratory: Herpetology Program (February, 2011)
  3. Shupe, S. (2011) US Guide to Venomous Snakes and Their Mimics. Skyhorse Publishing, New York.
  4. Glaudas, X. and Winne, C.T. (2007) Do warning displays predict striking behaviour in a viperid snake, the cottonmouth (Agkistrodon piscivorus)? Canadian Journal of Zoology, 85(4): 574-578.
  5. SeaWorld - Florida cottonmouth (April, 2012)
  6. Florida Museum of Natural History (February, 2011)
  7. Klein, A.G. (2005) Water Moccasins. ABDO Publishing Company, Minnesota.
  8. Smithsonian Zoological Park (February, 2011)
  9. Lilywhite, H.B., Sheehey, C.M. and Zaidan, F. (2008) Pitviper scavenging at the intertidal zone: An evolutionary scenario for invasion of the sea. Bioscience, 58(10): 947-955.
  10. Roth, E.D. (2005a) Buffer zone applications in snake ecology: a case study using cottonmouths (Agkistrodon piscivorus). Copeia, 2: 339-402.
  11. Rose, F.l., Simpson, T.R., Ott, J.R. and Manning, R.W. (2010b) Use of space by the western cottonmouths (Agkistrodon piscivorus) inhabiting a variable-flow stream. The Southwestern Naturalist, 55(2): 160-166.
  12. Hill, J.G. and Beaupre, S.J. (2008) Body size, growth, and reproduction in a population of western cottonmouths (Agkistrodon piscivorus leucostoma) in the Ozark Mountain of northwest Arkansas. Copeia, 1: 105-114.
  13. Glaudas, X., Andrews, K.M., Willson, J.D. and Gibbons, J.W. (2007) Migration patterns in a population of cottonmouths (Agkistrodon piscivorus) inhabiting an isolated wetland. Journal of Zoology, 271: 119-124.
  14. Whitfield Gibbons, J. and Dorcas, M.E. (2002) Defensive behaviour of cottonmouths (Agkistrodon piscivorus) toward humans. Copeia, 1: 195-198.
  15. Roth, E.D. and Johnson J.A. (2004) Size-based variation in antipredator behaviour within a snake (Agkistrodon piscivorus) population. Behavioural Ecology, 15(2): 365-370.
  16. Eskew, E.A., Willson, J.D. and Winne, C.T. (2009) Ambush site selection and ontogenetic shifts in foraging strategy in a semi-aquatic pit viper, the Eastern cottonmouth. Journal of Zoology, 227: 179-186.
  17. O’Shea, M. (2008) Venomous Snakes of the World. New Holland Publishers, London.
  18. Glaudas, X., Winne, C.T. and Fedewa, L. (2006) Ontogeny of anti-predator behaviour habituation in cottonmouths (Agkistrodon piscivorus). Ethology, 112: 608-615.
  19. Vincent, S.E., Herrel, A. and Irschick, D.J. (2004a) Ontogeny of intersexual head shape and prey selection in the pit-viper Agkistrodon piscivorus. Biological Journal of the Linnean Society, 81: 151-159.
  20. Linzey, D.W., and Clifford, M.J. (1981) Snakes of Virginia. University of Virginia Press, Virginia.
  21. Roe, J.H., Kingsbury, B.A. and Herbert, N.R. (2003) Wetland and upland use patterns in semi-aquatic snakes: Implications for wetland conservation. Wetlands, 23(4): 1003-1014.
  22. (February, 2011)
  23. US Environmental Protection Agency (February, 2011)
  24. UNESCO World Heritage Convention (February, 2011)
  25. National Park Service (February, 2011)
  26. Ramsar Convention (February, 2011)