Water snakes are common reptiles found in aquatic environments across North America. Not all water snakes are venomous, and accurate identification is important for both public safety and conservation.
Venomous Water Snakes
The primary venomous water snake in North America is the Cottonmouth (Agkistrodon piscivorus), also known as the Water Moccasin. This semi-aquatic pit viper is found in the southeastern United States, inhabiting swamps, marshes, ponds, lakes, and streams. Adult cottonmouths measure between 2 and 4 feet long, with a thick, heavy body that is often uniformly dark brown or black, though younger individuals may display distinct dark crossbands.
When threatened, cottonmouths display a defensive posture, coiling their bodies and opening their mouths wide to reveal the strikingly white interior, earning them their name. They may also vibrate their tails and release a musk. While their venom can be potent, cottonmouths are not aggressive and typically bite humans only when provoked, such as when stepped on or handled.
Non-Venomous Water Snakes
Many non-venomous water snakes, particularly those belonging to the Nerodia genus, are often mistaken for venomous cottonmouths due to their similar habitats and defensive behaviors. Common species include the Northern Water Snake (Nerodia sipedon). These snakes are largely aquatic, spending significant time in or near water sources like rivers, lakes, and ponds.
Nerodia species vary in appearance but are heavy-bodied, growing up to 4 feet or longer, with colors ranging from brown, gray, often with darker bands or blotches. When confronted, non-venomous water snakes may flatten their heads and bodies to appear larger, strike repeatedly, or release a musky odor. Although their bite can be painful, it is not venomous and poses little risk to humans.
Distinguishing Characteristics
Differentiating between venomous cottonmouths and non-venomous water snakes involves observing several key physical and behavioral cues. Cottonmouths possess a triangular head, noticeably wider than their neck due to venom glands. In contrast, non-venomous water snakes have a more oval-shaped head that blends smoothly with their body, though they can flatten their heads defensively to mimic a triangular shape.
A reliable indicator is the shape of the pupils: cottonmouths, being pit vipers, have vertically elliptical pupils, while non-venomous water snakes have round pupils. Cottonmouths also have a loreal pit between their eye and nostril, absent in non-venomous water snakes. When viewed from directly above, a cottonmouth’s eyes are obscured by a brow ridge, whereas water snake eyes are more visible.
Observing swimming behavior can also provide a clue; cottonmouths swim with most of their body floating on the water’s surface, with their head held at a 45-degree angle. Non-venomous water snakes, conversely, typically swim with their bodies mostly submerged, only their heads visible above the water. While both types of snakes have keeled (ridged) scales, cottonmouths have a darker, more uniform coloration as adults, with crossbands that narrow towards the backbone, unlike broader bands or squarish blotches on non-venomous water snakes.
Safe Encounters and Bite Protocol
When encountering a snake, observe from a distance and never attempt to handle, harass, or provoke. Most snakes, including cottonmouths, prefer to avoid confrontation and will retreat. Avoiding disturbing their habitat can also minimize unexpected encounters.
If a snake bite occurs, seek immediate medical attention if the bitten area changes color, swells, or becomes painful. Call emergency services promptly.
While waiting for medical help, remain still and calm. Remove any jewelry or tight clothing from the bitten limb before swelling begins. Clean the bite area with soap and water, and cover it with a clean, dry bandage.
Avoid attempting to suck out venom, applying a tourniquet, cutting the wound, or applying ice, as these can cause further harm. Remember the snake’s color and shape for identification, but do not attempt to catch or trap it.