The water moccasin, also known as the cottonmouth (Agkistrodon piscivorus), is a venomous snake found across the southeastern United States. This semi-aquatic viper lives primarily in wetlands, swamps, and other aquatic habitats, including rivers, lakes, and marshes. Accurately identifying this snake is important for personal safety and helps distinguish it from non-venomous water snakes.
Physical Characteristics
Water moccasins have several distinct physical features. They typically have a broad, triangular-shaped head that is noticeably wider than their neck, a result of their prominent venom glands. Their pupils are elliptical, resembling a cat’s eye. Between each eye and nostril, water moccasins have heat-sensing pits, which allow them to detect warm-blooded prey and predators.
These snakes are relatively large, often ranging from 30 to 48 inches long. They have a thick, heavy body compared to their length, differentiating them from more slender water snakes. Their coloration varies widely, from dark olive to brown or black, often displaying darker crossbands. A dark stripe often extends from the eye to the corner of the jaw, and their snout may appear pale or yellowish. The underside is generally lighter, sometimes with dark blotches.
Distinctive Behaviors
Water moccasins exhibit specific behaviors. When feeling threatened, they often perform a characteristic “gaping” display, opening their mouth wide to reveal the strikingly white, cotton-like interior. This defensive posture is the origin of their common name, “cottonmouth.”
Their swimming posture is also distinctive. Water moccasins typically swim with most of their body floating on top of the water, with their head held elevated. This differs from many non-venomous water snakes, which tend to swim with only their head visible above the surface, with the rest of their body submerged. When approached or cornered, water moccasins are more likely to stand their ground, sometimes coiling their body and vibrating their tail, rather than fleeing immediately.
Common Look-Alikes
Many non-venomous water snakes are frequently mistaken for water moccasins. Differences in head shape are key: water moccasins have a distinctly triangular head with a narrow neck, while non-venomous water snakes typically have a more rounded or oval head that blends smoothly into their body. However, some non-venomous water snakes can flatten their heads when threatened to appear more triangular, which can cause confusion.
Pupil shape offers a reliable distinction: water moccasins have vertically elliptical (cat-like) pupils, whereas non-venomous water snakes have round pupils. Heat-sensing pits are another key difference. Water moccasins possess these pits between their eye and nostril, which are absent in non-venomous water snakes.
Regarding swimming, water moccasins float higher on the water’s surface, while non-venomous water snakes are often more submerged. While water snakes may also flatten their bodies or strike when defensive, they do not exhibit the characteristic white mouth gaping display of the water moccasin. Although color patterns can be similar, water moccasins may have hourglass-shaped crossbands that are wider at the bottom, while water snakes often have bands that are wider on top.
Encountering a Water Moccasin
If you encounter a water moccasin, maintaining a safe distance is important. Stay at least 6 feet away from the snake. Never attempt to handle, harass, or capture any snake, especially if its identity is uncertain, as most snake bites occur when people try to interact with them.
Allow the snake to move away on its own, observing it from a distance. If a snake is in an area where it poses an immediate concern, such as inside a home or a frequently used public space, contact local animal control or a professional snake removal service. These professionals are equipped to safely handle and relocate venomous snakes.