Cottonmouth Confusion

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Published on: Jun. 2, 2004

Last revision: Nov. 16, 2010

Cottonmouth snake in defensive posture

as an endangered species in the state.

The coloration of the western mud snake has probably saved its life many times. Though it inhabits the same swampy areas of southeast Missouri as the cottonmouth, it is black with a distinctly red belly. The red coloration extends up onto the sides of the snake and is quite visible, making it easy to differentiate this snake from a cottonmouth.


Many people get confused when trying to identify this venomous snake. Even the name can be confusing. The cottonmouth is also called water moccasin, lowland moccasin, trapjaw and gapper. All of these names refer to the western cottonmouth, Agkistrodon piscivorus.

Adult cottonmouths are dark colored, ranging from olive-brown to black. Their bellies are cream colored and have dark brown or black blotches. Adults have a white upper lip.

Also, adults are heavy bodied, with a head noticeably wider than the neck. Young cottonmouths do not resemble adults. They are lighter in color and have 10 to 15 crossbands on their back. The tip of the tail is yellow in newborns. As with all venomous snakes in Missouri, cottonmouths have elliptical pupils, like those of a cat. They also have a visible pit between the nostril and the eye.

While it is true that venomous snakes have arrowhead shaped heads (due to the position of the venom glands at the rear of the jaw), this can be difficult to ascertain in the field. Remember that even a non-venomous snake may flatten its head and neck when it feels threatened in an attempt to discourage an aggressor. This can make it appear to have a diamond-shaped head.

The behavior of a snake can be a clue to its identity. When in the water, cottonmouths tend to swim with their heads held high, making their backs protrude above the surface of the water. When threatened, they open their jaws wide, a posture called gaping, to display the cottony white lining of the mouth. No other snake does this.

Geography can also provide an important clue. Cottonmouths do not occur north of the Missouri River, and in the Ozarks their distribution is spotty, normally restricted to cool, spring-fed creeks and small rivers. In southeastern Missouri they occur in cypress swamps, oxbow lakes and drainage ditches.

Whether the snake you see is a cottonmouth or another species, snakes are an integral part of Missouri's wildlife community and play vital roles in their respective ecosystems. They are also protected by Missouri's Wildlife Code. While snakes can evoke irrational fear in those who encounter them, it is still unlawful to kill, harm or harass them.

Those who fear snakes often misinterpret their actions. A snake swimming toward you in the shallows isn't planning to attack you. It's either stalking minnows or frogs, or simply going somewhere. If one approaches you, toss a stick or stone in its general vicinity, and the snake usually will avoid you.

If you'd like to learn more about aquatic snakes in Missouri, visit your local nature center or conservation office to purchase a copy of The Amphibians and Reptiles of Missouri, by Tom R. Johnson.

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