The cottonmouth (Agkistrodon piscivorus) is a venomous pit viper native to the southeastern United States. Understanding its distinct characteristics is important for safety, as misidentification can lead to dangerous encounters. This article provides information to help distinguish the cottonmouth from other snakes.
Physical Appearance
Cottonmouths are stout, muscular snakes, typically 30 to 48 inches long, though some reach 74 inches. Their heads are distinctly broad and triangular, much wider than the neck, and feature large jowls. They possess heat-sensing pits between each eye and nostril. Their pupils are vertically elliptical, like a cat’s eye, and are often obscured by an overhanging brow ridge. A broad, dark band frequently runs through the eye.
Coloration varies significantly, ranging from dark brown or black to olive, with some displaying broad, dark crossbands. These patterns can become obscured or disappear as the snake ages, leading to a uniformly dark appearance in older adults. Juveniles are typically lighter and more boldly patterned with distinct reddish-brown crossbands, often possessing a bright, sulfur-yellow tail tip used to lure prey.
Behavioral Clues
When threatened, cottonmouths often display a “gaping” behavior, opening their mouths wide to reveal the strikingly white, “cottony” interior. This gives them their common name and serves as a warning signal, creating a startling contrast with their darker body.
Unlike many other snakes that flee, cottonmouths tend to stand their ground. This defensive posture is a notable behavioral difference from many non-venomous water snakes. They may coil their bodies and display their fangs as a defensive tactic.
In aquatic environments, cottonmouths are semi-aquatic. They often swim with most of their body floating on the surface of the water, heads held high and slightly tilted upwards. This differs from many non-venomous water snakes, which typically swim with their bodies submerged below the surface.
Distinguishing from Similar Species
Distinguishing cottonmouths from non-venomous water snakes (Nerodia genus) is important due to their resemblance. One key difference lies in their head shape; cottonmouths possess a blocky, triangular head distinctly wider than their neck, while water snakes typically have a more slender head that is not as clearly separated from their body. Water snakes may flatten their heads when threatened to appear more triangular, but their heads will still appear similar in width to their neck.
Another distinguishing feature is the shape of their pupils. Cottonmouths have vertical, cat-like pupils, whereas water snakes have round pupils. Cottonmouths are pit vipers, meaning they have heat-sensing pits between their eyes and nostrils, which water snakes lack. When viewed from above, the eyes of a cottonmouth are often not visible due to an overhanging brow ridge, a characteristic that differs from water snakes whose eyes are visible from above.
Their swimming posture also provides a clue; cottonmouths frequently float with most of their body on the water’s surface, while water snakes tend to swim with only their heads visible above the water line. While both can vibrate their tails as a defensive behavior, the cottonmouth’s characteristic white mouth display is absent in water snakes. Relying on a combination of these behavioral cues, rather than a single feature, is a more reliable approach to identification.
Preferred Environments
Cottonmouths are found throughout the southeastern United States, from Virginia to Florida, and west to central Texas and southern Illinois and Indiana. They are typically associated with aquatic and wetland habitats within this range.
These snakes commonly reside in swamps, marshes, ponds, lakes, ditches, and slow-moving streams. They prefer locations with dense vegetation or debris near water, providing cover and hunting opportunities. While primarily semi-aquatic, they can occasionally venture away from permanent water sources. They are active both day and night, often foraging after dark during warmer months.