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Cottonmouth Confusion

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Published on: Jun. 2, 2004

Last revision: Nov. 16, 2010

Cottonmouth snake in defensive posture

"Uh-Oh! I think I just saw a snake in the water!"

Those words have needlessly ended a lot of fishing trips. Some people are so spooked by water snakes that the mere sight of one puts an abrupt end to any outing. Some uninformed outdoorsmen even go out of their way to kill them.

Many people falsely believe that any snake seen in or near the water is a water moccasin, also known as a cottonmouth. Along with cottonmouths, there are seven different species of non-venomous, semi-aquatic snakes found in our state and in most of Missouri. These non-venomous water snakes vastly outnumber the much feared cottonmouths, and they are the ones that usually frighten anglers and other stream lovers.

Most of Missouri's non-venomous snakes that are mistaken for cottonmouths belong to a single genus, Nerodia. Missouri is home to five species within this genus, and they share some interesting characteristics. All five primarily eat fish and amphibians. They don't have venom, but they put up quite a bluff when cornered. When threatened, they flatten their head and neck in order to look larger. They also bite and are known to release a pungent musk from a gland near their tail.

Admittedly, it can be difficult to identify a snake when you unexpectedly encounter one in the wild, especially if it is in the water. The following snakes are the ones most often mistaken for cottonmouths.

Northern Water Snake

(Nerodia sipedon)

The northern water snake is the most common semiaquatic, non-venomous snake in Missouri. Ranging statewide, it often shares habitat with cottonmouth snakes and is the snake most often misidentified as a cottonmouth. This snake is brown to orange. The bands crossing its back are darker than those on a cottonmouth. Its belly is cream colored with irregularly spaced half-moons or spots of orange or red.

On a warm spring day it wouldn't be unusual to see half a dozen northern water snakes while you're out fishing. You might even see one with its head protruding from the water like a periscope.

Diamond-Backed Water Snake

(Nerodia rhombifer)

This is the largest species of water snake found in our state. The Missouri record is 51 inches long. The nonvenomous, diamond-backed water snake ranges across large sections of Missouri, but it is not found in the Ozarks or extreme northern Missouri. It prefers the swamps, oxbow lakes and marshes common in the Bootheel and along the state's big rivers. In early summer and fall you may see them basking on rocks and logs, but during the heat of July, August and September they are mostly nocturnal.

This snake differs from cottonmouths by having a series of dark brown blotches along its back that are connected in a chain-like pattern.

Yellow-Bellied Water Snake

(Nerodia erythrogaster)

As an adult, this medium-size, non-venomous snake ranges from 30 to 48 inches long. Like the diamond backed water snake, it inhabits the still waters of swamps, ponds and oxbow lakes. It does not live in the Ozarks, either. In eastern Missouri, it ranges from the Bootheel in the south as far north as Pike County, just above St. Louis. It can also be found in roughly the western third of the state.

Adults of this species can be identified by their gray to greenish gray or brownish black color. The adults lack any distinct pattern along their backs. The belly of the snake is yellow with no markings.

Broad-Banded Water Snake

(Nerodia fasciata)

In Missouri, this species is restricted to lowland swamps and oxbow lakes of the Bootheel. Adults average from 22 to 36 inches long. Non-venomous broad banded water snakes are easily identified by wide brown or black bands separated by a cream yellow color.

Graham's Crayfish Snake

(Regina grahamii)

This snake is found statewide except in the Ozarks. Adults range from 18 to 28 inches long. These non-venomous snakes are very secretive. They eat mainly softbodied crayfish and prefer still or barely moving water, such as ponds, slow streams and marshes.

Many are killed simply because they are found near the water and believed to be cottonmouths, but these inoffensive creatures are reluctant to bite even when handled.

Unlike cottonmouths, this snake is brown with a yellowish stripe along its side. A faint tan stripe may be present along its back. Its belly is cream colored and has a very faint row of gray dots down the midline.

Other Semi-Aquatic Snakes

Though usually not mistaken for cottonmouths, there are two other semi-aquatic, non-venomous snakes found in Missouri: the Mississippi green water snake (Nerodia cyclopion) and the western mud snake (Farancia abacura).

The Mississippi green water snake is indigenous to southeast Missouri. It is not often seen, let alone mistaken for a cottonmouth. In fact, the snake hasn't been seen in Missouri since 1994 and is listed 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.

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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