The water moccasin, also widely known as the cottonmouth (Agkistrodon piscivorus), is a venomous snake found in the southeastern United States. This semi-aquatic reptile inhabits various wetland environments, including swamps, marshes, and slow-moving streams. Identifying this species accurately is important for safety.
Key Physical Characteristics
Water moccasins are characterized by their robust and muscular bodies. Adults typically measure between 2 to 4 feet in length, though some individuals can grow larger, occasionally exceeding 6 feet. They possess a thick girth relative to their length.
The coloration of a water moccasin can vary significantly, ranging from dark olive, brown, or tan to almost entirely black in older adults. Younger snakes often display more distinct patterns of darker crossbands against a lighter background, which tend to fade with age. The belly is usually lighter, with dark or brownish-yellow blotches.
A distinctive feature is their broad, triangular head, which is noticeably wider than their neck due to prominent venom glands. A dark stripe often extends from the eye to the corner of the jaw. Their pupils are elliptical, resembling a cat’s eye, distinguishing them from many non-venomous snakes with round pupils.
Water moccasins, like other pit vipers, possess heat-sensing pits located between their eyes and nostrils. These pits detect minute temperature differences, aiding in warm-blooded prey detection, especially in low light conditions. The scales covering their bodies are keeled, giving them a rough texture.
Behavioral and Habitat Identification Cues
Water moccasins are semi-aquatic snakes. They are commonly found in freshwater habitats such as cypress swamps, river floodplains, and heavily vegetated wetlands. They may also inhabit brackish water environments.
When swimming, water moccasins tend to float with most of their body on the surface, with their head elevated above the water. This differs from many non-venomous water snakes, which typically swim with only their head visible above the surface.
When threatened, water moccasins exhibit a defensive display. They may coil their body and open their mouth wide, revealing a stark white interior. This behavior, which gives them the common name “cottonmouth,” serves as a warning. They may also vibrate their tail, like a rattlesnake, and release a musky odor.
These snakes frequently bask on logs, rocks, or branches along the water’s edge. They can be active during the day or night, though they may forage more actively after dark, particularly in warmer seasons. They are known to remain still rather than flee when approached, relying on camouflage.
Distinguishing from Look-Alikes
Many non-venomous snakes are often mistaken for water moccasins, especially various species of water snakes from the genus Nerodia. Both are found near water and have similar dark colorations, but key differences exist. Water snakes typically have more slender bodies and longer, thinner tails compared to the thick, heavy-bodied water moccasin.
A primary distinction lies in the head shape and pupil type. Water moccasins have a distinctly broad, triangular head and elliptical (cat-like) pupils. In contrast, water snakes have narrower heads that are often not much wider than their necks, and they possess round pupils. When threatened, water snakes may flatten their heads to appear more triangular, but their heads still appear flattened rather than thick and blocky.
Unlike water moccasins, non-venomous water snakes lack the heat-sensing pits between their eyes and nostrils. Their defensive behaviors also differ; while water snakes may bite and release musk, they do not typically perform the open-mouthed “cottonmouth” display. Observing multiple characteristics (head shape, pupil shape, heat pits, and swimming style) is important for accurate identification.