The confusion surrounding aquatic snakes is common, but the answer is clear: true water snakes, belonging to the genus Nerodia, are non-venomous. Misidentification and concern stem from a single, highly venomous snake that shares the same aquatic habitat in the Southeastern United States. This dangerous look-alike is often mistakenly grouped with harmless water snakes, leading to unnecessary fear.
Characteristics of Non-Venomous Water Snakes
The Nerodia genus includes numerous species, such as the Northern Water Snake (Nerodia sipedon) and the Brown Water Snake (Nerodia taxispilota). These heavy-bodied snakes are largely aquatic, found near permanent freshwater sources like lakes, rivers, swamps, and ponds. Their coloration is variable, often brown, gray, or reddish, with dark blotches or bands for camouflage.
Nerodia species primarily eat fish and amphibians, capturing prey with strong jaws and sharp teeth rather than venom. When disturbed, their instinct is to retreat quickly into the water. If escape is impossible, they defend themselves aggressively, though their bite is non-venomous. Defensive behaviors include flattening their body and head to appear larger, expelling a foul-smelling musk, and biting repeatedly if handled.
The Venomous Snake Often Mistaken for a Water Snake
The source of the confusion is the Cottonmouth, or Water Moccasin (Agkistrodon piscivorus), North America’s only semi-aquatic pit viper. This highly venomous species is found exclusively in the Southeastern United States, inhabiting slow-moving waters like marshes, swamps, and ditches, sharing the environment with harmless water snakes. Its common names derive from its threat display, where it gapes its mouth to expose the stark white lining inside.
Cottonmouths are stout-bodied, typically reaching 30 to 42 inches as adults, often appearing uniformly dark brown or black when older. Their venom is hemotoxic, causing local tissue destruction, pain, swelling, and internal bleeding. Although a bite is rarely fatal, it causes severe tissue damage and requires immediate medical attention. This pit viper is active day and night, feeding on fish, amphibians, small mammals, and other snakes. When confronted, the Cottonmouth tends to hold its ground rather than flee, a behavioral contrast to the non-venomous water snake.
Key Differences for Identification
Distinguishing between the non-venomous water snake (Nerodia) and the venomous Cottonmouth (Agkistrodon piscivorus) requires observing key physical and behavioral traits.
Head Shape
The Cottonmouth, a pit viper, possesses a large, thick, blocky head that is noticeably wider than its neck, giving it a triangular appearance. Non-venomous water snakes generally have a more slender, rounded head that is not dramatically separated from the body. However, Nerodia species can flatten their heads when threatened, temporarily mimicking the triangular shape, which complicates field identification.
Pupils and Facial Features
A reliable difference is found in the eyes: Cottonmouths have elliptical, vertical pupils, a common feature among pit vipers. Nerodia water snakes have round pupils. Additionally, Cottonmouths possess a deep, heat-sensing pit located between the eye and the nostril, a feature absent in non-venomous water snakes.
Body Posture and Swimming Style
When swimming, a Cottonmouth typically keeps its entire body, or at least its head, high above the water’s surface, appearing to float. Conversely, the non-venomous water snake swims with its body mostly submerged, with only its head usually visible above the waterline. On land, Cottonmouths are known for their heavy, stout bodies, while water snakes tend to be more slender for their length.
Tail and Other Behaviors
Cottonmouths have a relatively short, thick tail, and their subcaudal scales (the scales under the tail) are typically a single row. Nerodia water snakes have a longer, thinner tail and feature a double row of subcaudal scales. When agitated, the venomous snake may vibrate its tail rapidly, a behavior not observed in the harmless water snake.
What to Do in Case of a Snake Encounter or Bite
The most effective safety protocol upon encountering any snake is to maintain a safe distance and leave it undisturbed. Snakes, whether venomous or not, generally try to avoid interaction and should be given the right-of-way to retreat. Never attempt to capture, handle, or kill a snake, as most bites occur during interaction.
If a bite occurs and there is any possibility it was from a venomous species, call emergency medical help immediately. While waiting for help, the person should remain calm and still, as movement can cause venom to travel more quickly. The bitten limb should be kept still and below the level of the heart, if possible, to slow the spread of potential venom. Promptly remove any rings, watches, or constricting clothing from the affected area, as swelling will begin quickly.
Traditional remedies must be avoided entirely. Do not:
- Apply a tourniquet.
- Cut the wound.
- Attempt to suck out the venom.
- Apply ice.
The wound should be gently cleaned with soap and water and loosely covered with a clean dressing until medical professionals can administer appropriate care, which may include antivenom.