garter snake, harmless snake of the genus Thamnophis, abundant from Canada to Central America. There are many common species; members of most species are about 2 ft (60 cm) long. Most garter snakes are striped or banded lengthwise, and some are spotted between the stripes. Less aquatic as a group than the related water snakes, they are found near water in dry country and are widely distributed in moist regions. They prey on cold-blooded animals, chiefly frogs, toads, small fish, and earthworms. Females bear live young in large litters, sometimes numbering 50 or more. The common garter snake of the NE United States, Thamnophis sirtalis, varies in color and pattern but is usually blackish or brownish with three yellow stripes. The ribbon snake, T. sauritus, is a very slender garter snake that prefers wet places. Garter snakes are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Squamata, family Colubridae.