Northern water snake

Northern water snake
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Colubridae
Subfamily: Natricinae
Genus: Nerodia
Species: N. sipedon
Binomial name
Nerodia sipedon
(Linnaeus, 1758)
Subspecies

4, see text

Synonyms

The northern water snake (Nerodia sipedon) is a species of large, nonvenomous, common snake in the Colubridae family that is native to North America.

Description

The northern water snake can grow up to 135 cm (4 ft 5 in) in total length.[2] Per one study, average total length of females was 81.4 cm (2 ft 8 in) while that of males was 69.6 cm (2 ft 3 in).[3] Per known studies of this species in the wild, adult females can weigh between 158.9 and 408 g (5.61 and 14.39 oz) in average body mass while the smaller male can average from 80.8 to 151 g (2.85 to 5.33 oz).[4][5][6][7] The largest females can weigh up to 560 g (20 oz) while the largest males can scale 370 g (13 oz).[8][9] They can be brown, gray, reddish, or brownish-black. They have dark crossbands on their necks and dark stripes and blotches on the rest of their bodies, often leading to misidentification as cottonmouths or copperheads by novices. They darken as they age. Some will become almost completely black. The belly of this snake also varies in color. It can be white, yellow, or gray. Usually it also has reddish or black crescents.

Water snakes are non-venomous and harmless to humans, but superficially resemble the venomous Water Moccasin and are often killed un-necessarily as a result of this mistaken identity. The two can be easily distinguished by morphological traits: the water snake has a longer, more slender body and a flattened head the same width as the neck with round pupils and no heat-sensing pits. The Water Moccasin has a fatter body, a wedge-shaped head with prominent venom glands that is wider than the neck, cat-like pupils and heat-sensing pits between the eyes and the nostrils.[10]

Subspecies

Ordered alphabetically.[1]

Geographic range

It is found throughout eastern and central North America, from southern Ontario and southern Quebec in the north, to Texas and Florida in the south.[11] It has been introduced in California where it is considered an invasive species likely to compete with native giant garter snakes Thamnopis gigas.[12]

Behavior

Northern water snake basking west of Ottawa, Ontario

They are active during the day and at night. They are most often seen basking on rocks, stumps, or brush. During the day, they hunt among plants at the water's edge, looking for small fish, frogs, worms, leeches, crayfish, salamanders, small birds and mammals. At night, they concentrate on minnows and other small fish sleeping in shallow water. The Lake Erie water snake subspecies, Nerodia sipedon insularum, was once endangered, but now benefits from the introduction of the round goby, an invasive species, which now comprises up to 90% of its diet.

The Northern Water Snake is extremely common over most of its range and is frequently seen basking on stream banks, from which it dives into the water at the slightest disturbance. It is quick to flee from danger, but if cornered or captured, it usually will not hesitate to defend itself. Large specimens can inflict a painful bite.

Reproduction

Northern water snakes mate from April through June. They are ovoviviparous (live-bearers), which means they do not lay eggs like many other snakes. Instead, the mother carries the eggs inside her body and gives birth to free living young, each one 19–23 cm (7.5–9.1 in) long.[13] A female may have as many as thirty young at a time, but the average is eight. They are born between August and October. Mothers do not care for their young; as soon as they are born, they are on their own.

Defense against predators

Northern water snakes have many predators, including birds, raccoons, opossums, foxes, snapping turtles, and other snakes and people. They defend themselves vigorously when they are threatened. If they are picked up by an animal, or person, they will bite repeatedly, as well as release excrement and musk. Their saliva contains a mild anticoagulant, which can cause the bite to bleed more but poses little risk to humans.

Hibernation

Northern water snakes often share winter dens with copperheads and black rat snakes.

Habitats

Muskrat houses and beaver lodges are good places to find water snakes, which like to hide among the sticks and plant stems. They live near lakes, ponds, marshes, rivers, and canals; just about anywhere there is freshwater.

The Lake Erie water snake subspecies (Nerodia sipedon insularum), which occurs mainly on the lake's western islands offshore from Ohio and Ontario, recovered to the point where on August 16, 2011 the U.S. Fish and Wildlife Service removed it from the Federal List of Endangered and Threatened Wildlife. The subspecies was first listed as threatened in 1999 after a decline due to eradication by humans, as well as habitat loss and degradation. When initially listed, the subspecies’ population had dropped to only 1,500 adults. Endangered Species Act (ESA) protections for the snake included designation of 300 acres of inland habitat and 11 miles of shoreline for breeding grounds. Ironically, the introduction of an invasive species, the Eurasian round goby (Neogobius melanostomus) into Lake Erie in the mid-1990s became a new food source for the Lake Erie water snake. By 2009, the population recovered to 11,980 snakes, safely exceeding the population minimum goal of 5,555 adult snakes required by the 2003 recovery plan. Monitoring will occur for 5 years following this delisting. The Lake Erie water snake is just the 23rd species to be removed from the list due to recovery.[14]

References

  1. 1 2 Nerodia sipedon, The Reptile Database.
  2. ↑ Northern water snake, Canadian Biodiversity.
  3. ↑ Weatherhead, Patrick J.; Barry, Frances E.; Brown, Gregory P.; Forbes, Mark R. L. (1995). "Sex ratios, mating behavior and sexual size dimorphism of the northern water snake, Nerodia sipedon". Behavioral Ecology and Sociobiology. 36 (5): 301–11. doi:10.1007/BF00167791.
  4. ↑ Jellen, Benjamin C.; Aldridge, Robert D. (2014). "It takes two to tango: Female movement facilitates male mate location in wild northern watersnakes (Nerodia sipedon)". Behaviour. 151 (4): 421–34. doi:10.1163/1568539X-00003128.
  5. ↑ Brown, Gregory P.; Weatherhead, Patrick J. (2000). "Thermal Ecology and Sexual Size Dimorphism in Northern Water Snakes,nerodia Sipedon". Ecological Monographs. 70 (2): 311–30. doi:10.1890/0012-9615(2000)070[0311:TEASSD]2.0.CO;2.
  6. ↑ Schulte-Hostedde, A. I.; Montgomerie, R. (2006). "Intraspecific variation in ejaculate traits of the northern watersnake (Nerodia sipedon)". Journal of Zoology. 270 (1): 147–52. doi:10.1111/j.1469-7998.2006.00101.x.
  7. ↑ Brown, Gregory P; Weatherhead, Patrick J (1999). "Demography and sexual size dimorphism in northern water snakes,Nerodia sipedon". Canadian Journal of Zoology. 77 (9): 1358–66. doi:10.1139/z99-112.
  8. ↑ Weatherhead, Patrick J.; Brown, Gregory P. (1996). "Measurement versus estimation of condition in snakes". Canadian Journal of Zoology. 74 (9): 1617–21. doi:10.1139/z96-179.
  9. ↑ King, R. B. (2002). "Predicted and observed maximum prey size - snake size allometry". Functional Ecology. 16 (6): 766–72. doi:10.1046/j.1365-2435.2002.00678.x.
  10. ↑ http://ufwildlife.ifas.ufl.edu/water_moccasin_watersnake_comparison.shtml[]
  11. ↑ Schmidt, K.P., and D.D. Davis. (1941). Field Book of Snakes of the United States and Canada. G.P. Putnam's Sons. New York. 365 pp. (Natrix sipedon, pp. 219-222, Figure 22. (map) + Plate 24 on p.344.)
  12. ↑ Rose, Jonathan P.; Miano, Oliver J; Todd, Brian D. (2013). "Trapping Efficiency, Demography, and Density of an Introduced population of Northern Watersnakes, Nerodia sipedon, in California". Journal of Herpetology. 47 (3): 421–427. doi:10.1670/12-119.
  13. ↑ Conant, Roger. 1975. A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Second Edition. Houghton Mifflin. Boston. 429 pp. ISBN 0-395-19977-8 (paperback). (Natrix sipedon, pp. 144-146 + Plate 20 + Map 99.)
  14. ↑ Endangered and Threatened Wildlife and Plants; Removal of the Lake Erie water snake (Nerodia sipedon insularum) From the Federal List of Endangered and Threatened Wildlife (PDF) (Report). 2011-08-16. Retrieved 2011-09-03.

Further reading

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