Common garter snake

Identification

The common garter snake usually has three light stripes running the length of a black, brown, grey or olive body³. The stripes may be yellow, white, blue, greenish or brown, and rows of dark spots between them can give a checkered look³. The side stripes sit on the second and third rows of scales up from the belly, and the lip scales have black bars^4,5. The scales are keeled, the head is a little wider than the neck, and the tongue is red with a black tip^3,5.

Colour varies widely across its range, and some populations include many all-black snakes³. Most adults are 46–66 cm long⁴, and the largest reach about 1.37 m³.

Distribution

This is one of North America’s most widespread snakes. It ranges from Florida to coastal Quebec and west to British Columbia and California, and reaches north into the Northwest Territories in Canada^1,3. It is largely absent from the dry south-west, but isolated populations live in the mountains of New Mexico and northern Mexico³.

Twelve subspecies are recognised, including the eastern, red-sided and San Francisco garter snakes^1,2. A 2023 genetic study did not support these traditional subspecies and instead found four broad geographic lineages².

Habitat

Common garter snakes live in meadows, marshes, woodland and hillsides, and they favour moist, grassy places^3,4. They are often found near water, such as the edges of ponds, lakes, ditches and streams, but can also live far from it⁴. They are among the snakes most often seen in suburbs and towns where there is cover such as boards, logs or rocks^3,4. In Illinois they even live on vacant city lots⁵.

Behaviour

Garter snakes are active mainly by day and can stay active at lower temperatures than most snakes³. They hibernate from about late October to March or April in burrows, rock piles and other cavities, and may come out to bask on mild winter days^3,5. Many gather to hibernate together³. At the Narcisse snake dens in Manitoba, tens of thousands of red-sided garter snakes overwinter in limestone caverns below the frost line⁶.

When threatened, a garter snake usually flees, often into water³. If cornered it coils, strikes and may bite, and if grabbed it writhes and releases a foul-smelling secretion³.

Diet

Common garter snakes eat earthworms, frogs, toads, salamanders, tadpoles and small fish^3,4. They also take leeches, slugs, snails, insects, crayfish and occasionally small mammals or young birds^3,5. They seem unaffected by the toxic skin of toads³. Some populations eat rough-skinned newts, which carry a powerful toxin, and these snakes have evolved resistance to it¹.

Reproduction

The common garter snake gives birth to live young³. Mating starts in spring as soon as the snakes leave hibernation, and in Manitoba a single female may be surrounded by up to 100 males in a “mating ball”^3,6. Females can store sperm until it is needed³. Litters of 10–40 young are typical, but up to about 80 have been recorded, born from late July to October^3,5. The newborn snakes are 12.5–23 cm long and get no care from their mother³.

Venom and medical significance

The common garter snake is not dangerous to people, and its reputation as a harmless snake is well deserved^3,6. Its saliva may be mildly toxic to small prey, which helps it handle them³. In one published case, a 13-year-old’s hand became swollen and bruised after a long, chewing bite; tests were normal, recovery was quick and later bites caused no symptoms⁷. Such reactions are very rare³.

Conservation

The common garter snake is listed as Least Concern on the IUCN Red List (assessed in 2007 and published in 2015)⁸. It is one of the most abundant snakes in the eastern United States, partly because it does well in towns and suburbs³. Even so, pesticides, habitat loss, water pollution and over-collection for the pet trade have reduced some populations³. The San Francisco garter snake, a subspecies, has been listed as endangered in the United States since 1967³.

Similar species

The common garter snake is most easily confused with other harmless garter and ribbon snakes, and with the lined snake⁵. Ribbon snakes are more slender, and their side stripes sit on the third and fourth scale rows rather than the second and third⁴. Ribbon snakes also lack the black bars on the lip scales that common garter snakes have⁴.

These differences are not a safe basis for handling any snake. Keep your distance from every snake you cannot identify.

In captivity

Common garter snakes tame easily and are sometimes kept as pets³. In captivity they usually live 6–10 years, and one lived to 20 years³. Collecting them for the pet trade has contributed to local declines, so wild garter snakes are best left where they are found³.