The genus of Nerodia (North American Watersnakes) belongs (together with (amongst others) the genus of Thamnophis and the genus of Natrix) to the family of Colubridae and the subfamily Natricinae.
The group of North American Watersnakes (Nerodia spp.) consists of relative heavy-bodied snakes that inhabit mostly moist and aquatic habitats and that live of aquatic prey, mostly fish and amphibians. They are all highly aquatic, although some species can wander for miles over land during rainy water. Most species can grow to 1.2 m (4 feet) or larger. The females of some species can even grow to 150 – 176.6 cm. N.taxispilota is the largest species. Only 2 species (Nerodia harteri and N.clarkii) stay below the 1 meter in total length.
Currently 9 different species and 24 different subspecies have been recognized within the genus of Nerodia (Gibbons & Dorcas , 2004). Nerodia clarkii, N. cyclopion, N.erythrogaster, N.fasciata, N.floridana, N.harteri, N.rhombifer, N.sipedon and N.taxispilota.
North American Watersnakes occur exclusively in North and Middle America but the focus of their distribution is Southeastern USA. Nerodia sipedon is the most northern species that also reaches (southeastern) Canada. 2 species , N.erythrogaster and N.rhombifer reach as far south as Mexico. N.clarkii is also found in northern Cuba. Most species are found at lower elevations. Nerodia sipedon is known to occur as high as 1463 m. They inhabit many different aquatic habitats like swamps, small creeks, large rivers, large lakes and even brackish and saltwater habitats.
Most species are brown or olive green, or some combination thereof with markings being brown, or black. Yellow or cream-colored accenting is common. A few species and subspecies possess red or reddish brown colors. They have eyes with round pupils. The scales are strongly keeled which gives them a rough appearance. Species like N. fasciata and N. sipedon display distinct banding, where other species, like N. taxispilota have blotching. N. rhombifer have a diamond-shaped pattern. Some species, like N. sipedon insularum are practically patternless. Stripes are relatively rare and only occur in some specimens of N.clarkii.
Gibbons, J.W. & M. E. Dorcas, 2004. North American Watersnakes. A natural history. University of Oklahoma Press, Norman. 1-438.