The common query about whether the brown water snake is dangerous stems from confusion between two different species that inhabit the same aquatic environments. Snakes commonly referred to as “brown water snakes,” belonging to the genus Nerodia, are non-venomous. Their presence near water, large size, and defensive behavior frequently lead to them being mistaken for the highly dangerous Cottonmouth. This misidentification is the primary reason for public concern.
The Definitive Answer Regarding Venom
The brown water snake is not a venomous species; it does not possess the modified salivary glands and specialized fangs required to inject toxins. Biologically, “venomous” applies to organisms that deliver a toxin through a bite or a sting, while “poisonous” refers to organisms harmful if ingested or touched. Since the brown water snake does not inject venom, it poses no threat of life-threatening envenomation.
Snakes in the Nerodia genus are defensive when cornered or handled. They bite readily, and because they have numerous small, sharp teeth used for gripping slippery fish, their bites can cause local bleeding and pain. While the bite is medically insignificant and requires only basic wound cleaning, the aggressive display often heightens fear and reinforces the mistaken belief that the snake is venomous. When threatened, they may also release a foul-smelling musk from glands near the base of the tail, a defense mechanism aimed at deterring predators.
Identifying the Non-Venomous Water Snake
Non-venomous water snakes, such as the Brown Water Snake (Nerodia taxispilota) or the Northern Water Snake (Nerodia sipedon), are robust snakes that can reach lengths of over four feet. Their coloration is highly variable, often featuring dark brown, gray, or black blotches or bands on a lighter background when young. As they age, their skin tends to darken significantly, obscuring the pattern and resulting in a more uniform brown or black appearance, which contributes to the “brown water snake” common name.
A distinguishing feature of these snakes is their round pupils, which are visible in adequate light. When cornered, water snakes often attempt to mimic a venomous snake by flattening their neck and head, giving it a broader, triangular shape. This bluffing behavior, combined with their tendency to strike repeatedly, is a reason for their frequent misidentification and persecution. They are often seen basking on logs or branches overhanging the water, ready to drop in and escape if disturbed.
Avoiding Dangerous Misidentification
Correctly distinguishing the non-venomous water snake from the venomous Cottonmouth or Water Moccasin (Agkistrodon piscivorus) is primary for safety. One distinction is observing the snake’s posture while swimming: the Cottonmouth floats high on the water’s surface with its entire body visible, whereas the non-venomous water snake swims with its body submerged, with only its head above the water.
The head shape offers another reliable clue: the Cottonmouth has a distinctly thick, blocky, triangular head that is noticeably wider than its neck, due to large venom glands. Non-venomous water snakes have a more slender head that blends into the neck with less definition. Cottonmouths possess vertical, slit-like pupils, resembling a cat’s eye, while the water snake has round pupils. The Cottonmouth, being a pit viper, also has a deep, heat-sensing loreal pit located between its eye and nostril, a feature absent in Nerodia species.