Water moccasins, also known as cottonmouths, are venomous snakes native to the southeastern United States. These semi-aquatic reptiles inhabit various wetland environments. Accurate identification is important for public safety and to avoid harming non-venomous species. This guide provides clear distinctions to help recognize them.
Key Physical Indicators
The water moccasin’s head is broad and distinctly triangular, resembling an arrowhead, and is much wider than its neck. This blocky appearance is partly due to venom glands. Unlike many non-venomous snakes, a cottonmouth’s eyes are not visible from above due to an overhanging brow ridge. Their pupils are elliptical or cat-like, appearing as vertical slits, especially in bright light, contrasting with the round pupils of most non-venomous water snakes.
Their body is stout and heavy, typically 30 to 48 inches long, though some can reach up to 74 inches. Their scales are keeled, meaning they have a raised ridge down the center, giving them a dull, non-reflective appearance. Coloration varies significantly, from dark brown, olive, or black, often with dark bands or blotches. These patterns can become obscured in older, darker individuals, appearing almost uniformly black. A dark facial band often extends from the eye to the jaw.
The bright white interior of its mouth gives the snake its common name “cottonmouth.” When threatened, the snake will often open its mouth wide, displaying this stark white lining as a warning. Juvenile cottonmouths are often lighter in color with more distinct reddish-brown bands and possess a bright yellow or sulfur-colored tail tip. This yellow tip is used to lure prey, such as frogs.
Behavioral Characteristics
Water moccasins exhibit specific behaviors that aid in their identification. When swimming, they often float with their entire body on the water’s surface, with their head held elevated. This swimming style differs from most non-venomous water snakes, which typically swim with only their head visible above the surface, their bodies largely submerged. While they can swim underwater, they frequently remain on the surface.
When threatened, cottonmouths typically do not flee immediately; instead, they often stand their ground. They may coil their body and open their mouths wide to display the white interior, serving as a clear warning signal. This defensive posture may also be accompanied by tail vibration, similar to a rattlesnake. While they have a reputation for aggression, they generally prefer to avoid confrontation and will often try to escape if given the opportunity.
Distinguishing from Look-Alikes
Misidentification of water moccasins is common, particularly with non-venomous water snakes like the Northern Water Snake (Nerodia sipedon) and Brown Water Snake (Nerodia taxispilota). Northern Water Snakes have more slender bodies and narrower heads that blend smoothly into their necks, without the distinct blocky shape of a cottonmouth. Their pupils are round, unlike the vertical slits of the water moccasin. While both can have dark bands, Northern Water Snakes often have squarish blotches, and their overall coloration tends to be lighter.
Brown Water Snakes also have more slender heads and bodies compared to the robust build of a cottonmouth. These non-venomous species lack the heat-sensing pits found between the eyes and nostrils of pit vipers like the water moccasin. When agitated, non-venomous water snakes may flatten their heads and bodies to appear larger and more triangular, which can lead to confusion. However, even when flattened, their head will still be a similar width to their neck, unlike the water moccasin’s distinctly wider head. Additionally, non-venomous water snakes do not display a bright white mouth interior as a warning.
Preferred Habitats and Range
Water moccasins are primarily found in aquatic environments throughout the southeastern United States. Their preferred habitats include swamps, marshes, ponds, lakes, ditches, and slow-moving streams. They are semi-aquatic, comfortable both in water and basking on land near these water sources. These snakes are often observed on logs, rocks, or branches at the water’s edge.
Their geographic range extends from southeastern Virginia, south through Florida, and west to eastern Texas, reaching north up the Mississippi River valley to southern Illinois and Indiana. They can also be found in brackish-water habitats and occasionally in saltwater. While they can wander from water, their presence is strongly associated with wetlands and other water bodies.