Reptiles
Water Snake
Nerodia · also called water snake, North American water snake
A water snake is the snake most often killed for being something it is not. Across North America, thick-bodied Nerodia water snakes basking by ponds and rivers are mistaken for venomous cottonmouths and clubbed on sight, even in states where cottonmouths have never lived. They have no venom. What they do have is a foul musk, a bite that bleeds, and a very bad attitude when grabbed.
Overview
The North American water snakes are the genus Nerodia, about ten species, close relatives of the garter snakes, found in and around almost any permanent fresh water in the eastern and central United States. They swallow fish and amphibians alive, hunting by day from the bank and by night in the shallows, and give live birth to litters of 20 to 40 in late summer.
Telling it from a cottonmouth
A water snake has round pupils, no facial heat pits, a narrow head, and swims with only its head above water. A cottonmouth has vertical pupils, deep facial pits, a blocky head, and floats high with its body on the surface, often gaping to show a white mouth lining. Range helps too — cottonmouths live only in the southeast.
When cornered
With no venom, a caught water snake strikes repeatedly, flattens its head, smears musk and faeces, and its saliva contains an anticoagulant that makes minor bites bleed freely. Left alone, it simply drops into the water and swims off.
Status
Most water snakes are Least Concern and the northern water snake is abundant. The Lake Erie water snake, once shot as vermin, fell to a few thousand, was listed as threatened, then recovered — helped by the invasive round goby becoming its main food — and was delisted in 2011.
Water Snake: common questions
How can I tell a water snake from a cottonmouth?
Look at the head, the eyes, and how the snake behaves in the water. A harmless water snake has a slender head only a little wider than its neck, round pupils, no pit between the eye and nostril, and round dark bands or blotches, and when swimming it holds just its head clear of the surface with its body submerged. A cottonmouth has a distinctly triangular, blocky head with a prominent brow, vertical cat-like pupils, a deep heat-sensing pit on each side of the face, and it swims buoyantly with much of its body riding on top of the water. A cottonmouth that feels threatened often coils, gapes to show the white lining of its mouth, and stands its ground, while a water snake almost always flees into the water or drops from its branch. Range also helps, as cottonmouths are confined to the southeastern United States.
Are water snakes venomous or dangerous?
No, water snakes have no venom and are not dangerous, but they are famously bad-tempered when caught. A cornered or grabbed water snake will flatten its head, strike again and again, bite hard and chew, and coat you in a rank-smelling musk and cloacal contents. The bite itself is shallow but the snake's saliva contains a mild anticoagulant, so the many small punctures bleed more than you would expect and look alarming. The wound needs washing and basic first aid and, as with any animal bite, watching for infection, but there is no toxin involved. Left alone, a water snake is not aggressive and will always choose to escape.
What is the difference between a water snake and a water moccasin?
Water moccasin is another name for the cottonmouth, which is a venomous pit viper, so a water moccasin is not a water snake at all. The confusion is entirely one of names and appearance. True water snakes are the non-venomous genus Nerodia, common across much of North America. The cottonmouth or water moccasin is a single venomous species of the southeast that also lives in and near water. Because dark, thick-bodied northern and banded water snakes look superficially like cottonmouths, people across the country report and kill cottonmouths in places, such as the northern states, where the venomous species has never occurred.
Do water snakes eat game fish, and are they bad for a pond?
They eat fish, but they are not a serious problem for a healthy pond or lake. Water snakes take whatever is easiest, which is mostly small, abundant, slow, or sick fish and a lot of frogs and tadpoles, and studies of their diet find they remove very few desirable adult game fish. On a natural water body their effect on fish populations is minor compared with birds such as herons and kingfishers. At a small stocked fish pond or a hatchery, where fish are crowded and cannot escape, a group of water snakes can take a noticeable number, and that is the one situation where they are genuinely unwelcome. Elsewhere they are a normal part of the wetland and help control invasive fish in some areas.