Reptiles
Northern Water Snake
Nerodia sipedon · also called common water snake, banded water snake
The northern water snake is one of the most common snakes in eastern North America, and one of the most frequently killed. It is harmless, but it is thick-bodied and dark, it lives at the water’s edge, and to a lot of people that adds up to cottonmouth.
Overview
Nerodia sipedon lives in and beside almost any permanent fresh water across eastern and central North America. It hunts fish and amphibians by day and night, and basks by day on branches, rocks, and docks, dropping into the water when disturbed.
The cottonmouth problem
Because it is heavy-bodied, dark, and often banded, it is constantly mistaken for the venomous cottonmouth where their ranges overlap, and killed. The differences: the water snake has a narrow head, round pupils, no heat pit, and swims with its body low in the water; the cottonmouth is the opposite on all four.
Harmless but feisty
It has no venom, but a cornered one flattens its head, strikes repeatedly, bites hard, and smears foul musk. Its saliva has a mild anticoagulant, so bites bleed freely. It gives live birth to 15 to 30 young in late summer.
Status
Least Concern and abundant, adaptable even to city canals. A Lake Erie island subspecies was once threatened and has recovered.
Northern Water Snake: common questions
Is the northern water snake venomous?
No. It has no venom and no fangs, and it is completely non-venomous. It is, however, quick to defend itself, and a large one that is cornered or picked up will flatten its head to look triangular, strike again and again, bite down and chew, and release a strong-smelling musk. Because its saliva contains a mild anticoagulant, a bite from a big water snake can bleed more than you would expect for the size of the wound, which adds to its fearsome reputation, but there is no venom involved and the bite is not medically serious beyond ordinary wound care.
How do I tell a water snake from a cottonmouth?
Look at the head and the way it swims. A northern water snake has a narrow head only a little wider than its neck, round pupils, and no pit between the eye and nostril, and when it swims most of its body is below the surface. A cottonmouth has a distinctly wide, angular, blocky head, vertical cat-like pupils, an obvious heat-sensing pit, and it swims with its head and much of its body riding high on the water. A cottonmouth that feels threatened also tends to hold its ground and gape to show the white lining of its mouth, while a water snake almost always flees into the water. From a safe distance, give any thick-bodied waterside snake the benefit of the doubt and leave it alone.
Why do people kill so many harmless water snakes?
Almost entirely because of the cottonmouth mix-up. In the parts of the southeastern United States where cottonmouths occur, many people believe any dark, heavy snake in or near the water is a cottonmouth, and northern and other Nerodia water snakes fit that image closely. The water snake's defensive display, flattening its head and striking, reinforces the impression. As a result huge numbers of harmless water snakes are killed every year, even though they are beneficial predators of fish and frogs and pose no danger. In much of the northern part of the range there are no cottonmouths at all, so a water snake there cannot be one.
Do northern water snakes eat game fish, and are they bad for a pond?
They eat fish, but they are not a real threat to a fishery. A water snake mostly takes slow, sick, injured, or very abundant small fish, along with a lot of frogs, tadpoles, and crayfish, and studies of pond and stream communities do not show water snakes suppressing game fish populations. In a balanced pond they are part of the natural predator community and help remove weak individuals. The instinct to kill them to protect the fishing is misplaced, and in most places these snakes are protected as native wildlife.