The inquiry about “Green Water Snakes” often stems from confusion between non-venomous water-dwelling species and the dangerously venomous Water Moccasin. It is important to first understand the distinction between “poisonous” and “venomous.” A snake is venomous if it injects toxins through specialized fangs, while it is poisonous if it releases toxins when ingested or touched. No North American water snake is poisonous.
Understanding the Non-Venomous Water Snakes
Snakes often labeled as “Green Water Snakes” belong to the genus Nerodia, including species like the Green Water Snake (Nerodia cyclopion) and the Florida Green Water Snake (Nerodia floridana). These non-venomous snakes rely on fish and amphibians in aquatic habitats. They are stout-bodied and can grow quite large, sometimes reaching over 4 feet in length.
These snakes are not aggressive but will readily defend themselves if cornered or handled. When threatened, a water snake often flattens its head and body to appear larger and more menacing, leading to misidentification as a venomous species. Although their bite is not medically significant, it can cause small puncture wounds that require cleaning to prevent bacterial infection.
Key Differences from Venomous Water Moccasins
Non-venomous Nerodia share habitats with the highly venomous Water Moccasin, also known as the Cottonmouth (Agkistrodon piscivorus). Identifying features are often subtle, but knowing the differences is important for safety. One reliable feature is the pupil shape: harmless water snakes have round pupils, while the Cottonmouth has vertically elliptical pupils, similar to a cat’s eye.
The venomous Cottonmouth has a distinctly thick, blocky, and triangular head, noticeably wider than its neck. This feature is accentuated by a prominent ridge or “brow” above the eyes that partially obscures them when viewed from above. In contrast, the non-venomous water snake’s head appears more flattened, and its neck is nearly the same width as its head, even when defensively flattened.
A primary behavioral difference is how the snakes swim. The Cottonmouth is known for swimming with most of its body on the water’s surface, giving it a floating appearance. Non-venomous water snakes typically swim with their bodies submerged, only lifting their heads out to breathe. Cottonmouths are pit vipers and possess heat-sensing pits located between the eye and the nostril, a feature absent in Nerodia species.
Safe Behavior Around Water Snakes
The safest approach when encountering any snake near water is to maintain a respectful distance and leave the animal alone. Trying to capture, handle, or kill any snake dramatically increases the risk of being bitten. Giving all snakes space is the best way to prevent an encounter, even though non-venomous bites are generally minor.
If a bite occurs and the snake is suspected to be venomous, immediate action is necessary. The affected person must remain calm and seek emergency medical attention by calling 911 or a local emergency number. While waiting for help, remove any rings, watches, or tight clothing near the bite site before swelling begins.
The bitten limb should be kept still and positioned neutrally, meaning it is not held above or below the heart. Avoid applying a tourniquet, cutting the wound, or attempting to suck out the venom, as these actions cause more harm than good. Antivenom is the only definitive treatment for venomous snakebites, making rapid transport to a hospital the most important step.