Pond and Lake Wildlife: Northern Water Snakes

A healthy pond or lake will attract all sorts of wildlife, including one of the most misunderstood animals, snakes. Of the 21 species of snakes in Pennsylvania, several may be seen around ponds and lakes. Three are considered aquatic. The most commonly encountered water snake in the state is the northern water snake (Nerodia sipedon sipedon). Why are they attracted to ponds? The natural attractions are simply water and food.

Northern water snakes live throughout Pennsylvania in ponds, swamps, marshes, and borders of lakes, rivers, and streams. They prefer slow-moving or standing water with available basking sites such as rocks, logs, and tree limbs. Emerging from hibernation in April, they are active day and night and are most active from May to July. They mate between April and June, with the females giving live birth to an average of 20 young per litter in late summer or early fall. They return to hibernation dens in crayfish burrows, bank burrows, rock crevices, vole tunnels, and hollow logs in mid-October.

A healthy pond provides a wide availability of prey for northern water snakes. They feed primarily on fish and frogs but will also eat other amphibians and occasionally crayfish, insects, small mammals, and carrion. Studies have shown they feed on weaker fish and generally do not harm fish populations. They are not venomous and are often mistaken for the venomous cottonmouth, a species that is actually absent from Pennsylvania. Of the snakes in Pennsylvania, they could be misidentified as eastern milk snakes or northern copperheads.

Northern water snakes are the largest of the three aquatic snakes in the state, reaching 24–50 inches in length. They have thick, heavy bodies, with the females topping the males in size. The background color varies from gray-brown to light brown. Their pattern consists of crossbands and blotches that vary from reddish brown to dark brown. The patterns are more obscure in older adults, making them more uniform in color. The varying colors and patterns often lead to mistaken identity. Northern water snakes have strongly keeled scales (raised along the center of the scale), unlike eastern milk snakes, which have smooth, glossy scales. Northern copperheads also have dark bands, similar to the pattern of northern water snakes. However, one way to distinguish the copperhead is the broad triangular head and narrow neck. The northern water snake’s head is more narrow, and the neck is not as defined. Perhaps the best way to identify the northern water snake is by noting its presence in an aquatic habitat and its large size.

Populations of northern water snakes are healthy. However, habitat loss and pollution are threats. An encounter with one may be startling, but know they are harmless pond dwellers. They can be feisty if threatened, so don’t bother them. If encountered, they will likely slither away very quickly. If you see one around your pond, take some time to observe it. They are excellent swimmers. You may see them patrolling the waters, swimming with just their head above water. If seen basking, remember they are performing an important life function—regulating their body temperature. Please do not kill them. Take some time to learn about, understand, and respect this misunderstood reptile. They have essential roles in the pond ecosystem and are not harmful to you, the pond, or its function.