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Common names for N. sipedon include banded water snake, black water adder, black water snake, brown water snake, common water snake, common northern water snake, eastern water snake, North American water snake, northern banded water snake, northern water snake, spotted water snake, streaked snake, water pilot, and water snake.
The common watersnake can grow up to 135 cm (4 ft 5 in) in total length (including tail). Per one study, the average total length of females was 81.4 cm (2 ft 8 in), while that of males was 69.6 cm (2 ft 3 1⁄2 in). From known studies of this species in the wild, adult females can weigh between 159 and 408 g (5 1⁄2 and 14 1⁄2 oz) typically, while the smaller male can range from 80.8 to 151 g (2 7⁄8 to 5 3⁄8 oz). The largest females can weigh up to 560 g (20 oz) while the largest males can scale 370 g (13 oz).
N. sipedon can be brown, gray, reddish, or brownish-black. It has dark crossbands on the neck and dark blotches on the rest of the body, often leading to misidentification as a cottonmouth or copperhead by novices. As N. sipedon ages, the color darkens, and the pattern becomes obscure. Some individuals become almost completely black. The belly also varies in color. It can be white, yellow, or gray; usually, it also has reddish or black crescents.
The common watersnake is nonvenomous and harmless to humans, but superficially resembles the venomous cottonmouth and is often killed unnecessarily as a result of this mistaken identity. The two can be easily distinguished by morphological traits; the watersnake has a longer, more slender body and a flattened head the same width as the neck, round pupils, and no heat-sensing pits. The cottonmouth has a fatter body, a wedge-shaped head with prominent venom glands that are wider than the neck, cat-like pupils, and heat-sensing pits between the eyes and the nostrils.
Colubrid snakes also have flat scales on their heads, while vipers all possess smaller, rugose scutes.
- N. s. insularum (Conant & Clay, 1937) – Lake Erie watersnake
- N. s. pleuralis (Cope, 1892) – midland watersnake
- N. s. sipedon (Linnaeus, 1758) – northern watersnake
- N. s. williamengelsi (Conant & Lazell, 1973) – Carolina watersnake
The common watersnake is found throughout eastern and central North America, from southern Ontario and southern Quebec in the north, to Texas and Florida in the south. Since at least 1992, this species, along with N. fasciata, has been introduced in California, where they are considered invasive species likely to compete with native giant garter snake Thamnophis gigas.
N. sipedon is active during the day and at night. It is most often seen basking on rocks, stumps, or brush. During the day, it hunts among plants at the water's edge, looking for small fish, frogs, worms, leeches, crayfish, salamanders, small birds, and mammals. At night, it concentrates on minnows and other small fish resting in shallow water. It hunts using smell and sight. The Lake Erie watersnake subspecies, N. s. insularum, was once endangered, but now benefits from the introduction of the round goby, an invasive species, which constitutes up to 90% of its diet.
The common watersnake is 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 does not hesitate to defend itself. Larger specimens can inflict a painful bite.
The common watersnake mates from April through June. It is ovoviviparous (live-bearing), which means it does 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 1⁄2–9 in) long. A female may have as many as 30 young at a time, but the average is eight. They are born between August and October. Mothers do not care for their young.
Defense against predators
N. sipedon has many predators, including birds, raccoons, opossums, foxes, snapping turtles, other snakes, and humans. The common watersnake defends itself vigorously when threatened. If picked up by an animal or person, it will bite repeatedly, and release excrement and musk. Its saliva contains a mild anticoagulant, which can cause the bite to bleed more, but poses little risk to humans.
Muskrat houses and beaver lodges are good places to find the common watersnake, which likes to hide among the sticks and plant stems. N. sipedon lives near lakes, ponds, marshes, rivers, and canals.
The Lake Erie watersnake, 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 protections for the snake included designation of 120 ha (300 acres) of inland habitat and 18 km (11 mi) of shoreline for breeding grounds. 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 watersnake. 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 was to occur for 5 years following this delisting. The Lake Erie watersnake is just the 23rd species or subspecies to be removed from the list due to recovery.
N. sipedon swimming in Chesapeake Bay in the United States
Mature northern watersnake sunning itself near Battersea, Ontario
Hunting on a beach near Georgian Bay, Ontario
Northern watersnake swimming in pond Hayesville, North Carolina
Basking in the sun along French Creek, Pennsylvania
N. s. insularum on Kelleys Island
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