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NORTHERN WATER SNAKE

Nerodia sipedon sipedon


NORTHERN WATER SNAKEDescription: This is a moderately large, dark-colored snake usually seen in or near water. The tan, brown, or gray background color is typically overlaid by a variable pattern of black, dark brown, or reddish brown crossbands and blotches on the back and sides. Complete crossbands usually predominate on the forward third of the body, breaking up into smaller, often alternating "saddles" and side blotches towards the tail. The blotched pattern may become obscured by dark pigment over time, and older adult Northern Water Snakes can appear solid brown or black, particularly when their skin is dry. At least a hint of the blotched pattern is often visible when they are wet. The white, yellowish, or orangish belly is usually marked with a pattern of reddish brown half-moon-shaped spots, sometimes interspersed with, or grading into, grayish or brownish speckling. There are 21 to 25 scale rows at midbody; the scales are keeled, and the anal plate is divided. Total adult length: 61 to 140.5 cm (24 to 55.3 in).

Males are, on average, smaller than females, and have proportionally longer tails. In males the subcaudal (undertail) scutes number from 66 to 84, with the tail length representing 23 percent to 29 percent of the total length; females have from 42 to 77 subcaudal scutes, and their tails make up 20 percent to 25 percent of their total length.

Newborn Northern Water Snakes range in length from 19 to 27 cm (7.5 to 1 0.6 in). They are more distinctly patterned than adults, with black or reddish brown bands and blotches on a grayish or tan background.

Note: The above description applies to the wide-ranging subspecies Nerodia sipedon sipedon, which retains the name Northern Water Snake. Nerodia sipedon inhabiting islands in western Lake Erie (the Put-In-Bay Archipelago) are recognized as a separate subspecies, the Lake Erie Water Snake (Nerodia sipedon insularum). Typical specimens of this subspecies are pale gray, grayish olive, or grayish brown in dorsal coloration and lack the dark-blotched pattern of a typical Northern Water Snake. The belly is white to yellowish. The average size is slightly larger than N. s. sipedon (maximum total length for a female = 144 cm; 56.7 in). Populations of water snakes on the various islands often contain a fairly high percentage of intergrade specimens (having varying degrees of pattern development), along with smaller percentages of the "pure" patternless form and still smaller numbers of the "typical" dark, banded form. The existence of this race may represent a classic example of natural selection, since it seems to more closely match the rocky (limestone) shoreline habitats in these islands (and may thus be less visible to predators, such as gulls) than the darker mainland form. However, the apparent ability of the snakes to move from the mainland to and between the islands and the high proportion of intergrade and "normal" patterned specimens on the islands has led some herpetologists to question the recognition of this subspecies.

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Confusing Species: The Copper-bellied Water Snake has a plain red or orange belly, sometimes invaded by dark brown or black color along the edges of the ventral scales. Kirtlandís Snake has a pink or red belly with a row of black spots down each side. Garter and ribbon snakes have lengthwise dorsal stripes and a single (undivided) anal plate. The Eastern Milk Snake has a black-on-white "checkerboard" belly pattern, smooth body scales, and a single anal plate.


Map of Northern Water Snake's distribution in Michigan.Distribution and Status: The Northern Water Snake ranges from eastern Maine west through Nebraska and portions of eastern Colorado, south to Oklahoma and Arkansas and east to Virginia and the Carolinas. It occurs throughout the Great Lakes region, except for the northern and western portions of the Lake Superior drainage basin. The Lake Erie Water Snake is found on certain islands of western Lake Erie in Ontario and Ohio, from Pelee Island and East Sister Island south through the Bass Islands to Kelleys Island. They also occur sparingly on the Catawba-Marblehead Peninsula, in Ottawa County, Ohio. An additional subspecies (Nerodia sipedon pleuralis) extends the speciesí range from southern Indiana and Illinois to eastern Louisiana and the Florida panhandle.

Northern Water Snakes can be common to abundant in some places, though many local populations have been reduced or eliminated by persecution or pollution. The Lake Erie Water Snake, once locally abundant in its limited range, has experienced drastic reductions in numbers on many Lake Erie islands in recent years.

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Belly scales of Northern Water SnakeHabitat and Ecology: This snake will live in or near most permanent bodies of water, including rivers, streams, sloughs, lakes, ponds, bogs, marshes, swamps, and impoundments. Fairly open, sunny locations with ample cover and basking sites are preferred (e.g., low overhanging shrubbery, clumps of cattails or other vegetation, beaver and muskrat lodges, exposed root systems, logs, or piles of rocks, driftwood, or human-generated debris). They often frequent waterside structures such as wooden docks, boathouses, piers, bridge supports, earthen or rock dams and causeways, spillways, and flowing culverts.

Northern Water Snakes occasionally move overland (most often juveniles dispersing to new habitat) but are usually found in, or immediately adjacent to, water. These snakes are mostly active during daylight hours in spring and fall but may adopt nocturnal habits in summer. When not basking or foraging they tend to remain hidden beneath logs, flat rocks, boards, or other cover. Older juveniles and adults are often seen basking on shoreline debris but dive into the water at the slightest disturbance. A frightened snake will usually hide itself near the bottom for a few minutes, then resurface and swim parallel to the shoreline. If repeatedly threatened, however, most will eventually retreat to deeper water and may remain submerged for over an hour if necessary. Over most of their Great Lakes range these snakes hibernate from October to April, with the actual period of dormancy dependent on local climatic conditions. The colder months are passed (often with numbers of their own and other snake species) in mammal or crayfish burrows, rock crevices, overbank root systems, or other sheltered sites near their summer habitat.

Northern Water Snakes eat mostly "cold-blooded" prey; small fish make up the largest part of the diet, followed in frequency by frogs, tadpoles, aquatic salamanders, and crayfish. Insects and earthworms are occasionally consumed, particularly by young snakes, while small mammals (mice, shrews) are rarely taken. Food is located by sight (particularly moving objects) and by odor. They seek prey underwater by actively probing into clumps of vegetation or under rocks or other submerged objects and may charge open-mouthed into schools of small fish. On the other hand, they sometimes capture frogs or fish after a slow, deliberate stalk. These snakes will eat carrion, including partially decomposed fish. The Lake Erie Water Snake seems to feed mostly on dead and dying fish that wash into its rocky shoreline habitat.

Natural enemies of the Northern Water Snake include larger predatory fish, Bullfrogs, Snapping Turtles, other snakes (Racers, larger water snakes), hawks, herons (and other wading birds), raccoons, skunks, mink, and otters. Humans are the most serious enemies of these snakes in many places. A Northern Water Snake will try to escape from a potential predator whenever possible but can aggressively defend itself when necessary. If cornered or seized, it may flatten its head and body and strike out repeatedly at the perceived enemy. While not venomous, its tiny recurved teeth can cause pinpoint wounds or scratches that bleed freely and are, at least briefly, quite painful. In addition, this snake can release surprising quantities of a noxious, musky-smelling substance from its cloaca, which may discourage a predator (or human captor) not already deterred by its biting attack.

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Reproduction and Growth: Courtship and mating occur in spring, typically mid-April to mid-June, and may take place on land or in water. A courting male will crawl over the female, matching her body position and movements, and rub his chin along her back, sometimes with occasional spasmodic jerks of his head or body. He must twine his tail around the femaleís and bring their cloacal openings into contact to effect copulation. It is not uncommon for two or more males to simultaneously court the same female; competing males may try to shove each other out of position but apparently do not bite or otherwise injure each other.

Most females give birth to their young in August or September. Reported litter size for the species ranges from 4 to 99 (most often 15 to 40), with larger females generally producing proportionally larger litters than smaller ones. Growth is rapid in the young snakes, some of which may nearly double their length in their first growing season (though the average increase is closer to about 50 percent per year). Growth rate slows considerably at sexual maturity, which is attained in two to three years. A Northern Water Snake lived over nine years and seven months in captivity, but the average life span in the wild is unknown.

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Conservation: This is surely one of the most persecuted snake species in the Great Lakes region. People often kill Northern Water Snakes out of fear or ignorance, or in the belief that they reduce the numbers of game fish. Although these snakes will bite if cornered or seized, they are harmless if left alone. They are sometimes called "water moccasins" and erroneously assumed to be venomous. (The true "water moccasin" or Cottonmouth, Agkistrodon piscivorus. does not occur within the Great Lakes basin.)

Northern Water Snakes have little or no impact on sport fishing in natural bodies of water. They tend to eat smaller, slower-moving or injured fish, mostly species less desired by humans, and may actually improve fishing in some places by feeding on fish stunted by overpopulation, and by consuming dead or diseased fish. Being opportunistic feeders, Northern Water Snakes can be a problem in fish hatcheries and on fish farms, where their removal may be justified.

Unwarranted persecution, combined with shoreline development, has led to local extirpation of Northern Water Snakes in some areas. The Lake Erie Water Snake has proven particularly vulnerable to these problems, and they now are absent, or present only ih low numbers, on many of the islands where they were once common. Public education programs, combined with legal protection, would greatly benefit remaining populations of this unique race.

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The above information has been reproduced or complied from the field guides with permission to use such material from the author, James Harding, for the sole use of educating the public on native Reptiles and Amphibians. The field guides used were:

  • Michigan Snakes: A Field Guide and Pocket Reference (1989; rev. 1998) by J.A. Holman, J.H. Harding, M.M. Hensley, and G.R. Dudderar, Michigan State University Cooperative Extension Service, East Lansing, E-2000.
  • Amphibians and Reptiles of the Great Lakes Region by J.H. Harding, (2000) University of Michigan Press, Ann Arbor.

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