Many people wonder about the difference between a “water moccasin” and a “cottonmouth,” often using the terms interchangeably. Understanding this relationship, along with key identification features, is important for safely navigating environments where these snakes live.
Understanding the Names
The terms “water moccasin” and “cottonmouth” both refer to the same venomous snake, scientifically known as Agkistrodon piscivorus. This species is the only venomous semi-aquatic snake in North America. The name “cottonmouth” originated from a distinctive defensive behavior where the snake opens its mouth wide, revealing a stark white interior.
While “water moccasin” is another widely used common name, particularly in some rural areas, “cottonmouth” is often preferred to avoid confusion with other non-venomous water snakes. Regardless of the name used, Agkistrodon piscivorus is a pit viper found throughout the southeastern United States.
Identifying the Cottonmouth
Cottonmouths possess several physical characteristics that aid in their identification. Their head is notably broad and triangular, appearing distinct from their neck. When viewed from above, their eyes are often not visible, unlike many non-venomous snakes.
A defining feature of cottonmouths is their vertically elliptical pupils, similar to a cat’s eye. They also have heat-sensing pits located between their eyes and nostrils. Adult cottonmouths are heavy-bodied snakes, typically ranging from 30 to 48 inches in length, but some individuals can exceed 6 feet. Their coloration varies, from dark brown or olive to almost entirely black, often with darker crossbands that may become obscured with age. Juvenile cottonmouths have a more pronounced pattern of reddish-brown crossbands and a distinct sulfur-yellow or greenish tail tip, which they wiggle to attract prey.
When threatened, cottonmouths commonly exhibit their namesake defensive display by opening their mouths to show the white lining. They may also vibrate their tail or release a musky scent as warnings. This display is a warning, not an aggressive action, and snakes will often attempt to retreat before resorting to a bite.
Habitat and Behavior
Cottonmouths are semi-aquatic snakes, often found in or near freshwater environments such as swamps, marshes, ponds, lakes, and slow-moving streams. They are also known to inhabit brackish waters and can be found on barrier islands. While typically associated with water, they are not strictly aquatic and can travel overland, sometimes found a mile or more away from a water source.
These snakes are opportunistic predators, consuming a diverse diet that includes fish, amphibians, small mammals, birds, and other reptiles. Cottonmouths are not inherently aggressive; their primary response to a perceived threat is typically to flee. Studies show that bites are rare and usually occur when the snake is directly provoked or handled.
During cooler months, they may bask on logs or rocks near the water’s edge and can be active during the day, though they frequently forage at night in warmer periods.
Distinguishing From Similar Snakes
Many non-venomous water snakes, particularly those in the Nerodia genus, are frequently mistaken for cottonmouths. Several key differences can help distinguish between these species. Non-venomous water snakes typically have narrower heads that are not as distinct from their necks, though they may flatten their heads when threatened to appear more triangular.
Another important distinction lies in their pupils; non-venomous water snakes have round pupils, unlike the vertical, elliptical pupils of the cottonmouth. When swimming, non-venomous water snakes generally keep most of their body submerged, with only their head visible, differing from the cottonmouth’s more buoyant, surface-floating posture. Additionally, water snakes lack the characteristic white mouth display that gives the cottonmouth its name. Cottonmouths also tend to have thicker, heavier bodies compared to the more slender build of many non-venomous water snakes of similar length.