Common garter snake

Thamnophis sirtalis

SUBFAMILY

Natricinae

TAXONOMY

Coluber sirtalis Linnaeus, 1758, Canada. Eleven subspecies are recognized.

OTHER COMMON NAMES

French: Couleuvre rayèe, serpent-jarretière; German: Gewöhnliche Strumpfbandnatter; Spanish: Culebra-listonada común.

PHYSICAL CHARACTERISTICS

The common garter snake is a relatively slender snake generally reaching about 28 in (70 cm) in length. Color varies greatly across the wide geographic range of this species, but in most populations the snake exhibits three longitudinal yellow stripes. The ground color may be dark brown, olive green, or red, sometimes with black patches.

DISTRIBUTION

This species is widely distributed across North America, including the eastern half of the continent, the northern Great Plains and northern Rocky Mountains, and the Pacific Coast.

Some Canadian populations extend far north, one reaching the southern Northwest Territories.

HABITAT

Common garter snakes are found in a wide variety of habitats, including marshes, fields, woodlands, and forest edges. This species is often found in association with water.

BEHAVIOR

In general this snake is diurnally active, with a long activity season. It is active year round in the southern part of the range, and even at extreme northern localities it has been reported to be active for five months out of the year. Individuals in northern populations may travel long distances from their hibernation sites to their summer foraging habitats.

FEEDING ECOLOGY AND DIET

This species forages actively on a wide variety of prey, including both vertebrates and invertebrates. Common prey include earthworms, fishes, and frogs, but a host of other prey also are eaten, occasionally including small mammals or birds.

REPRODUCTIVE BIOLOGY

This snake is viviparous, with litter size varying geographically. The usual litter size is about 10-15 young, although lower numbers are common in some northern populations, and an average of over 30 was recorded for a population in Maryland. Populations in Manitoba, Canada, are well known for the enormous aggregations of males seeking to mate upon emergence from hibernation. The males, which are smaller, emerge earlier, so females are courted by large numbers of waiting males.

CONSERVATION STATUS

Not listed by the IUCN. The San Francisco garter snake (T. s. infernalis, previously known as T. s. tetrataenia) is the only snake in the United States listed as Endangered by the U.S. Fish and Wildlife Service. Habitat loss is primarily responsible for its decline. In Manitoba, Canada, where the red-sided garter snake (T. s. parietalis) aggregates by the thousands in communal hibernacula, the populations were once threatened by overcollection for commercial purposes. A ban on export of garter snakes from Manitoba was imposed in 1991.

SIGNIFICANCE TO HUMANS

Because of their abundance and ease of maintenance in captivity, common garter snakes are used for a variety of laboratory studies and are also maintained as pets. ♦

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