The terms “cottonmouth” and “water moccasin” often cause confusion. This article aims to clarify their meaning, provide accurate identification tips, and offer guidance for safe interactions with this snake. Understanding these distinctions is important for personal safety and for fostering a better appreciation of wildlife.
One Snake, Two Names
“Cottonmouth” and “water moccasin” are indeed common names for the same venomous snake, Agkistrodon piscivorus. This pit viper belongs to the subfamily Crotalinae, placing it in the same group as rattlesnakes and copperheads. The name “water moccasin” can lead to confusion with non-venomous water snakes, which is why some scientists prefer “cottonmouth.”
Identifying the Cottonmouth
The cottonmouth (Agkistrodon piscivorus) possesses several distinct physical and behavioral characteristics that aid in its identification. It is a stout, heavy-bodied snake, typically 30 to 48 inches long, though some can grow larger. Its head is notably broad and triangular, distinctly set apart from a narrower neck due to large venom glands. Pupils are vertical and slit-like, and a dark stripe extends from the eye to the jaw. Cottonmouths also have heat-sensing pits between the eye and nostril.
Coloration can vary significantly from olive to brown or black, often with broad crossbands that may become obscure as the snake ages. Juvenile cottonmouths display more vivid patterns and have a bright yellow-tipped tail, which they may use to lure prey. When threatened, the cottonmouth performs a characteristic defensive display by coiling its body and opening its mouth wide, revealing the strikingly white, “cotton-like” interior—this behavior is the origin of its common name. This semi-aquatic viper is often found basking on logs or branches near water bodies like swamps, marshes, ponds, and slow-moving streams. When swimming, cottonmouths keep most of their body floating on the surface with their head held at an upward angle.
Distinguishing From Other Water Snakes
Distinguishing cottonmouths from non-venomous water snakes, primarily Nerodia species, is important. A primary difference is head shape; non-venomous water snakes have narrower heads that blend smoothly with their neck, unlike the cottonmouth’s broad, triangular head. Water snakes also have round pupils, contrasting with the cottonmouth’s vertical, slit-like pupils.
Swimming posture offers another distinguishing clue: cottonmouths swim with most of their body floating on the surface. In contrast, non-venomous water snakes swim with their bodies submerged, with only their heads visible above the waterline. While non-venomous water snakes will bite if provoked, their bite is not venomous. Water snakes may flatten their heads when threatened, attempting to mimic the triangular shape of a venomous snake, but they lack the heat-sensing pits found on cottonmouths. Cottonmouths also have a distinct white stripe along their upper lip, which is absent in Nerodia species.
Safe Encounters and Prevention
A cautious approach is required when encountering any snake. Always maintain a safe distance and never attempt to catch, handle, or kill a snake. Cottonmouths are not aggressive and prefer to retreat or use their defensive mouth display as a warning rather than biting. They will not chase people.
Observing them from a distance allows for appreciation without provoking a reaction. If a bite occurs, seek immediate medical attention.
To prevent encounters, be aware of your surroundings, especially in aquatic habitats where cottonmouths live. Wear appropriate footwear when walking in areas with dense vegetation or near water. Look carefully before stepping over logs, rocks, or into thick undergrowth, and before reaching into areas where a snake might be concealed. Reducing potential hiding spots around homes, such as clearing debris, woodpiles, and tall grass, can also deter snakes. Maintaining good drainage and well-maintained water features also makes an area less attractive to snakes.