American Bullfrog

Northern Watersnake Joe Crowley

Northern Watersnake
(Nerodia sipedon sipedon)

Other names: common watersnake, Natrix sipedon sipedon

The watersnakes, and other harmless snakes that bear live young, were included in the family Colubridae but recently have been placed in the family Natricidae.

Characteristics

Northern watersnakes are brown or dark brown with faint alternating dark (sometimes reddish) horizontal banding on the back and sides. Young snakes are greyish with pronounced brown banding, and they become darker as they age until the patterning can barely be seen. The belly is lighter in colour, often white or tan with dark red, tan or brown crescent-shaped spots. The scales of this species are keeled (ridged down the centre), which gives the snake a rough, rather than a shiny, appearance. Adults generally reach a length of between 60 and 110 centimetres, but some individuals may be even larger. The Lake Erie watersnake (N. s. insularum) is a subspecies of the northern watersnake but is found only on islands in western Lake Erie and on its southern shore in Ohio.

Similar Species

The northern watersnake may be confused with the gray ratsnake, eastern foxsnake, milksnake, eastern hog-nosed snake, eastern massasauga and Lake Erie watersnake. The gray ratsnake is black with faint blotches, whereas the northern watersnake is dark brown with faint banding. The eastern foxsnake has a yellow to light brown body with brown blotches down its back and two alternating rows of smaller blotches along the sides. The milksnake has red or reddish brown blotches along its back and sides with a distinct black outline around each blotch. The eastern hog-nosed snake has a distinct upturned snout. The eastern massasauga has a rattle on a blunt tail, a vertical pupil and a triangular head. Distinguishing northern watersnakes from many Lake Erie watersnakes is almost impossible, but their ranges do not overlap. Lake Erie watersnakes are found only on islands in western Lake Erie, including Pelee Island, whereas northern watersnakes are not present on those islands.

Habitat

The northern watersnake can be found in and around almost any permanent body of fresh water within its range, including lakes, rivers and wetlands. Rarely far from shoreline habitats, these snakes can be found in shoreline vegetation, basking on rocks and logs, or in other open habitats along the edges of the water or under rocks along the shoreline. Northern watersnakes hibernate underground in dens or crevices, or in beaver lodges.

Biology

Northern watersnakes breed in the spring after emerging from hibernation. Breeding aggregations of up to 12 males and one female have been reported. Females develop the eggs within their bodies and give birth to live young in late summer or early autumn. In Ontario, females give birth to 10 to 20 young. Often a clutch of hatchlings has more than one father. The size of the hatchlings is related to the mother’s size but averages about 18 centimetres. In Canada, these snakes reach maturity in three to four years.

The northern watersnake eats fish and amphibians, hunting for its prey along the water’s edge or underwater. It is an excellent swimmer and can be found up to three metres below the surface of the water and several kilometres from shore. Although this snake usually swallows small prey head first upon capture, it may carry large fish to shore before consuming them. The northern watersnake frequently basks in the open, often in large groups.

This species is active in the day and at night. Like the Lake Erie watersnake, the northern watersnake is curious and not as wary of humans as many other snakes are. It may even approach swimmers as it investigates the source of ripples in the water (which could be from a fish or other prey) or if it mistakes them for a floating log or other debris it can hide in or bask on. Northern watersnakes are harmless but will bite in self-defence if they are captured. Although often their bite is not even felt, it can cause mild bleeding because the snake’s saliva contains an anticoagulant.

Threats & Trends

The northern watersnake is widespread and abundant within its range in Canada and is one of the most commonly seen snakes around lakes. There are few threats to this species, but waterfront construction and development, as well as water pollution, affect both its habitat and food sources. Habitat loss, road mortality and persecution by humans also negatively affect the northern watersnake.

Current Status & Protection

The northern watersnake is currently listed as Not at Risk under the Ontario Endangered Species Act, 2007 and Not at Risk under the federal Species at Risk Act. The species has also been designated as a Specially Protected Reptile under the Ontario Fish and Wildlife Conservation Act. These acts offer protection to individuals and their habitat. The habitat of this species is further protected in Ontario by the Provincial Policy Statement under the Planning Act. The International Union for Conservation of Nature has not assessed the global status of the northern watersnake. The species’ status was last confirmed in January 2010. Additional detail about legal protection for species at risk in Ontario is available on our Legal Protection page.

Learn more about reptile and amphibian conservation and what you can do to help these species on our Reptile and Reptile and Amphibian Stewardship page.

 

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Range

Northern Watersnake Range Map

Ontario range (click to enlarge)

Southern Ontario range (click to enlarge)

In Canada, the northern watersnake is limited to southern Ontario, south of Lake Superior, and extreme southern Quebec. This species occurs throughout the northeastern United States, and as far south as Arkansas and as far west as Colorado.

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