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By Anders Nielsen, Ph.d.
The Cottonmouth snake, or (A. piscivorus), is one that many refer to by names such as the Water Moccasin, or a combination of variations: Cottonmouth Moccasin, Highland Water Moccasin, and North American Water Moccasin.
The explanation for its name is the bright white lining of the mouth that it displays as a warning to predators and prey alike.
Cottonmouth snakes forage by ambushing, actively searching for, and hunting their prey. They commonly eat dead animals as a source of nourishment. Most often, when they encounter a prey, e.g. a rodent, they inject their venom into it, let it go for a while and then hunt it down when it is subdued by the venom
Their diet varies, although they rely heavily on fish. They eat small alligators, toads, birds, snails, and bird eggs. They also feed on smaller snakes, including their own species.
Juvenile cottonmouth snakes have the ability to attract potential prey by moving their tail, luring their prey closer.
Cottonmouth venom is more dangerous than most other types of snake venom. Deaths from cottonmouth occur once in a while. Its venom works by destroying blood cells and preventing the victims blood from clotting. Not lethal bites sometimes leads to amputations.
Cottonmouth snakes are strong swimmers and are primarily located in or close to water, where their prey resides. The Latin name piscivorus literally translates into "fish eater". However, their diets expand beyond merely fish.
A study by Himes (2004)3 showed that cottonmouth snakes also had a varied diet of non-fish food sources.
The water snake is relatively large, thick, and fat looking and displays broad, opaque bands along its body. Cottonmouths darken with age, and at some point, the bands become obscured. Similar to the Copperhead snake, these snakes have a slightly green hue on the tip of their tails. The Cottonmouth snake is the most aquatic of the Agkistrodon, although is able to survive as far as one mile away from water1.
The media has instilled in people an irrational fear of unprovoked attacks from Cottonmouth snakes, and other venomous snakes for that matter, but such fears are unsubstantiated. Studies have shown that Cottonmouths are unlikely to strike unless humans initially provoke it, or the snakes become directly handled.
One of the largest cottonmouth snakes (water moccasins) ever encountered was recently found in Florida. The video shows its characteristic triangular head typical of venomous species. The cottonmouth was 7 foot long. The news reporter tells that the weight of the snake is 87 pound. Luckily, that is not realistic for a cottonmouth. Cottonmouths are not aggressive, so just leave them alone if you encounter one.
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, you can find the location of the specific sub-species in the United States.
Cottonmouth snakes are difficult to distinguish from Water snakes, and numerous Water snakes are killed on suspicion alone of being Cottonmouth snakes. Here are three tips that will help you distinguish whether a snake is a Cottonmouth or a Water snake:
However, as a reader pointed out, Water snakes sometimes flatten their head so it appears to look triangular. This behavior has proven advantageous through evolution, as they then look like the dangerous Cottonmouths when this process occurs.
There are many different sub-species of Water snakes. Some of these species have since evolved to bear a closer resemblance to the Cottonmouth more than other sub-species.
Typically, water snakes inhabit the same habitats as cottonmouth snakes in a relationship referred to as sympatric. This term defines a relationship in which both species inhabit the same area, and do not divide the habitat between them. These habitats are always close to water.
Cottonmouth snakes mate annually every spring and, after a gestation period of three to four months, the female gives birth to up to 16 juvenile snakes. The neonates have an average length of 8 to 14 inches. The eggs hatch within the female body - this is described in the literature as ovoviviparity. Neonate Cottonmouths are venomous as juvenile.
Males typically fight one another for the right to mate with the females.
Characteristic features of juvenile Cottonmouths are their colored tails, which are used for luring prey closer.
In states like Virginia, where it is rather cold during the winter, the Cottonmouth snakes may hibernate for several months. In cold areas, hibernation is necessary even though it is dangerous as mortality rates during hibernacula are high. In addition, 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 of hibernation is wooded hillsides, also called bluffs, where they remain 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 deemed suitable for hibernation. 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 hibernacula - often a stump hole, or a hole left by decayed roots5.
In places like Florida and Texas, the Cottonmouth snakes may not hibernate at all.
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
Thanks to Terry, Lisa, Charles, Alan, and Jakob for giving me the permission to use their photos.
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