Garter snake is a common name for generally harmless, small to medium-sized snakes belonging to the genus Thamnophis in the family Colubridae. Native to North and Central America, species in the genus Thamnophis can be found from the subarctic plains of Canada to Costa Rica.
Garter snakes vary in total length (including tail) from 46 to 137 cm (18 to 54 in) and weigh approximately 140 g (5 oz). With no real consensus on the classification of species of Thamnophis, disagreement between taxonomists and sources such as field guides over whether two types of snakes are separate species or subspecies of the same species is common. Garter snakes are closely related to the genus Nerodia (water snakes), with some species having been moved back and forth between genera.
Garter snakes are present throughout most of North America. Their wide distribution is due to their varied diets and adaptability to different habitats, with varying proximity to water. However in the western part of North America these snakes are more aquatic than in the eastern portion. Garter snakes live in a variety of habitats, including forests, woodlands, fields, grasslands and lawns, but never far from water, often an adjacent wetland, stream or pond. This reflects the fact that amphibians are a large part of their diet. Garter snakes are often found near small ponds with tall weeds.