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Nerodia sipedonNorthern Water Snake

By Merritt Gillilland

Geographic Range

Northern water snakes are found in southern Ontario and the northeastern United States from Nebraska and Kansas in the west to the Atlantic coast and as far south as North Carolina and southern Missouri. (Harding, 1997)

Habitat

Northern water snakes utilize many different aquatic habitats, such as: rivers, streams, sloughs, lakes, ponds, bogs, marshes, and impoundments. They prefer open areas that provide many spots for them to bask in the sun and relatively still waters. They may move onto land, especially the juveniles, but they never go to far from the aquatic environment. When they are not basking or searching for prey items they can be found beneath flat rocks, logs, boards or other types of cover. Northern water snakes are the most common snakes near water sources throughout northeastern North America. (Harding, 1997)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

These are dark-colored snakes, brownish, tan or grayish in appearance. The back and sides have a series of square blotches alternating with each other that may merge to form bands. Adult snakes can appear solid brown or black, especially when dry. The belly is usually white, yellowish, or orangish with dark half-moon-shaped black edges. Juveniles have reddish brown saddles on a tan, brown, or gray background. Males are usually smaller than females. (Behler and King, 1979; Harding, 1997; Jordan, 1929; Tyning, 1990)

Scales are keeled and the anal plate is divided, with 21-25 scales at midbody.

Northern water snakes are medium to large snakes, ranging from 61 to 140 cm. They range from 19 to 27.3 cm at birth.

  • Sexual Dimorphism
  • female larger
  • Range length
    61 to 140 cm
    24.02 to 55.12 in

Reproduction

Male northern water snakes are able to reproduce when they are 21 months old. Female snakes begin to breed when they are three years old and produce a single litter each year. Most reproduction occurs while in or near their hibernation sites between mid-April and mid-June. Temperature and latitude may cause variation in these times. (Bauman and Metter, 1977)

During breeding, a male comes along side a female and rubs his chin along her back, occasionally giving a spasmodic jerk. He then twines his tail around hers and brings the cloacal openings into contact. Usually only one male copulates with a single female; on occasion there may be two. (Harding, 1997; Tyning, 1990)

Gestation can last anywhere from 3 to 5 months. Young snakes are born alive (not laid as eggs) from July to September. The litter ranges in size from 4 to 99 offspring. Larger females tend to have larger litters.

  • Breeding interval
    Northern water snakes mate once yearly
  • Breeding season
    April to June
  • Range number of offspring
    4 to 99
  • Range gestation period
    3 to 5 months
  • Average age at sexual or reproductive maturity (female)
    3 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    730 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    21 months
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    730 days
    AnAge

Female northern water snakes nurture and protect their young before they are born. Young water snakes become independent at birth, and are capable of hunting and caring for themselves.

  • Parental Investment
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Northern water snakes have been known to live up to 9 years and 7 months in captivity. Their lifespan in the wild is unknown.

  • Range lifespan
    Status: captivity
    115 (high) months
  • Average lifespan
    Status: captivity
    9.6 years
    AnAge

Behavior

Northern water snakes are only social during the fall and spring after overwintering. They can be found in groups at basking sites coiled together. For the most part they are solitary animals, especially in the warmer months. It is quite common to find northern water snakes sunning themselves during the warm part of days. They can be found on overhanging branches, walkways, beaver lodges, dried cattail stems, and many shallow areas in the water.)

Northern water snakes can be found during the day or at night, but are more active during the daylight hours. Because of their preference for aquatic habitats they are commonly mistaken for venomous water moccasins, Agkistrodon piscivorous. Northern water snakes are not venomous but they are aggressive and should always be treated with care and respect. (Tyning, 1990)

Communication and Perception

Northern water snakes probably communicate with each other primarily through touch and smell. They also use their sense of sight and detection of vibrations to locate prey.

Food Habits

Northern water snakes are carnivores and scavengers. They eat a variety of prey items, including amphibians (adults and tadpoles), fish (alive or dead), crayfish, large insects, leeches, other snakes, turtles, birds, and small mammals such as white-footed mice. They have been known to herd schools of fish or tadpoles to the edge of bodies of water where they can prey upon many at one time. Northern water snakes hunt both during the day and at night. They are not constrictors, they simply swallow their prey alive. (Tyning, 1990)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • fish
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • aquatic crustaceans

Predation

Northern water snakes often escape predators by swimming off across a body of water or by diving below the surface, where they anchor themselves to vegetation or logs. They usually remain submerged for about 5 minutes but are capable of remaining below water for an hour and a half.

When confronted, northern water snakes flatten their bodies and jaws and begin to strike and bite ferociously. They also release a foul-smelling musk and may defecate to discourage predators. When extremely agitated they will also regurgitate their last meal. Northern water snakes are preyed on by large snakes, such as milk snakes and racers, and by raccoons, skunks, and foxes.

  • Known Predators

Ecosystem Roles

Northern water snakes control the populations of their primary prey, including fish, amphibians, and other reptiles.

Economic Importance for Humans: Positive

Contrary to popular belief, northern water snakes are quite beneficial to fish populations. They feed on diseased and dying fish and help to control areas where overpopulation may exist and could stunt fish growth. This may actually help the sport fishing industry. (Harding, 1997)

Economic Importance for Humans: Negative

Northern water snakes could potentially be a problem for fish hatcheries and fish farms. (Harding, 1997)

Conservation Status

Northern water snakes are abundant throughout their range.

Other Comments

Snakes of this species are often killed by people who are afraid of them, and confuse them with venomous species, such as rattlesnakes. Northern water snakes will bite if you bother them, but they are not venomous.

Contributors

Allison Poor (editor), University of Michigan-Ann Arbor.

Merritt Gillilland (author), Michigan State University, James Harding (editor), Michigan State University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

native range

the area in which the animal is naturally found, the region in which it is endemic.

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynous

having more than one female as a mate at one time

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Bauman, M., D. Metter. 1977. Reproductive cycle of the northern water snake, Nerodia sipedon (Reptilia, Serpentes, Colubridae). Journal of Herpetology, 11(1): 51-59.

Behler, J., F. King. 1979. The Audubon Society Field Guide to North American Reptiles and Amphibians. New York: Alfred A. Knoph, Inc..

Harding, J. 1997. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor, Michigan: The University of Michigan Press.

Jordan, D. 1929. Manual of the Vertebrate Animals. New York: World Book Company.

Tyning, T. 1990. Stokes Nature Guides: A guide to Amphibians and Reptiles. Boston, MA: Little, Brown and Company.

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