Cottonmouth snakes

The cottonmouth snake (Agkistrodon piscivorus) is also known under the name water moccasin, or a combination of names such as cottonmouth moccasin, highland water moccasin or North American water moccasin. However, the name cottonmouth snake is more precise as water moccasin can be many different types of snakes. It is a relatively large, thick-, and fat looking snake with wide, dark bands along its body. Cottonmouth darkens with age and at some point the bands become obscured. As copperheads they have a greenish tail-tip. The cottonmouth snake is the most aquatic of the Agkistrodon's, although it can be found as far as one mile away from water¹.

Some people fear unprovoked attacks from cottonmouth snakes, and other venomous snakes for that snake, but such fears are unfounded. Studies have shown that cottonmouths are unlikely to bite unless being picked up.

Sub species and geographic distribution

There are three subspecies of cottonmouth snakes: The Eastern cottonmouth snake (A. p. piscivorus), the western cottonmouth snake (A. p. leucostoma) and the Florida cottonmouth snake (A. p. conanti). In the table below it can be seen which subspecies are found in the US - and where.

Identification

Water snakes are difficult to discriminate from cottonmouth snakes, and often water snakes are killed on suspicion alone of being cottonmouth snakes. Three tips will help you see whether a snake is a cottonmouth or a water snake.

a) Water snakes have broad flat heads, whereas water snakes (Nerodia) have round heads.
b) Water snakes have round pupils, whereas cottonmouths have elongated pupils.
c) Water snakes have eyes on the rounded part of their head, whereas the cottonmouths eyes are on the side of their flattened heads.

Habitat

Cottonmouth snakes lives close to water.

Often, Northern water snakes inhabit the same habitats as cottonmouth snakes in a relationship called sympatry, where both species inhabits the same area, and do not split the habitat between them.

Diet

Cottonmouth snakes are good swimmers and are often found in or close to water where most of their prey is found. The Latin name piscivorus literally translates into fish eater. However, they do eat other food items as well. A study by Himes (2004)³ showed that cottonmouth snakes also had a varied diet of non-fish food sources.

Cottonmouth snakes forages by ambushing and by actively searching for and hunting prey. Sometimes they even feed on dead animals. Their diet is varied although they rely heavily on fish. They eat small alligators, toads, birds if they can be captured, snails and eggs from birds. They also feed on smaller snakes, including their own species. Younger cottonmouth snakes can attract potential prey by moving their tail, luring their prey closer.

Life-cycle and reproduction

Cottonmouth snakes mate every spring and, after a gestation period of three to four months, the female gives birth to up to 16 young snakes. The neonates have a size of 8 to 14 inches. The eggs hatch within the female body before the birth - this is called ovoviviparity. Neonate cottonmouths are venomous, and can take care of themselves right after birth.

Males may sometime fight each other for the right to mate the female.

A characteristic feature of juvenile cottonmouths is the colored tail used for luring prey closer.

Cotton in its mouth

The explanation for the name cottonmouth is the bright white lining of the mouth that it displays as a warning to anyone who gets to close.

Hibernation

In states like Virginia, where it is rather cold during the winter, the cottonmouths may hibernate for several months. In cold areas hibernation is necessary even though it is dangerous as mortality rates during hibernacula are high. Also, mortality during hibernacula in the winter may be the most important factor preventing viable populations of cottonmouths to spread north of Virginia².

The preferred place to hibernate is wooded hillsides, also called bluffs, where they stay in stump holes. Therefore, during early winter, it is possible to see cottonmouth snakes migrating from their swamps and rivers until they reach a place suitable for hibernation. Therefore, as pointed out by Glaudas et al. (2006)⁴, it is important that corridors exist between upland and wetland so that the cottonmouths can find places to hibernate.

During the winter the cottonmouths may lie coiled close to their hibernaculum - often a stump hole or a hole left by decayed roots⁵.

In places like Florida and Texas, the cottonmouth snakes there may not hibernate at all.

References

1. Gloyd, H.K. & Conant, R. Snakes of the Agkistrodon Complex: A Monographic Review (1990)
2. Blem, C.R. & BLEM, L.B. The Eastern Cottonmouth (Agkistrodon Piscivorus) at the northern edge of its range Journal of Herpetology 29(3) pp. 391-398 (1995)
3. Himes, J.G. The non-fish, vertebrate diet of sympatric populations of the cottonmouth Agkistrodon piscivorus and Northern Watersnake Nerodia sipedon Herpetological Review 35(2) pp. 123 (2004)
4. Glaudas, X. et al. Migration patterns in a population of cottonmouths (Agkistrodon piscivorus) inhabiting an isolated wetland. Journal of Zoology 271(2) pp. 119-124
5. Gibbons, J.W. & Dorcas, M.E. Snakes of the Southeast. (2005) University of Georgia Press

Acknowledgement

Thanks to Terry, Lisa, Charles, Alan, and Jakob for giving me the permission to use their photos.

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