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NATURAL HISTORY

GIANT GARTER SNAKE } Thamnophis gigas
FAMILY: Colubridae

DESCRIPTION: The giant garter snake reaches up 64 inches in length. Individual snakes vary in color from brownish to olive, with a checkered pattern of black spots, a yellow stripe down the center of the back, and light-colored stripes along the sides. The underside is cream to olive or brown.

HABITAT: Giant garter snakes inhabit natural and managed wetlands, low gradient streams, sloughs, ponds, small lakes, rice fields and associated waterways such as irrigation and drainage canals, and adjacent uplands.

RANGE: Sacramento and San Joaquin Valleys in California

MIGRATION: This species does not migrate.

BREEDING: Giant garter snakes breed from March through May, with males immediately searching for mates after emerging from winter retreats. Females give birth from late July through early September. Breeding resumes briefly during September.

LIFE CYCLE: Giant garter snakes emerge from over-wintering sites in the spring, when they begin foraging for food. Mating occurs in the spring and again briefly in the fall. By late fall, snakes will enter winter retreats, only emerging during winter to move or bask on warm days. Young snakes born in late summer immediately scatter into dense cover.

FEEDING: Giant garter snakes feed primarily on small fishes, tadpoles, and frogs and specialize in ambushing small fish underwater.

THREATS: The species is threatened by habitat loss and fragmentation, flood-control activities, changes in agricultural and land-management practices such as conversion of rice fields, predation from introduced species, pesticides and water pollution.

POPULATION TREND: More than 90 percent of the suitable habitat for this species has been eliminated. There are only 13 isolated populations of the giant garter snake remaining, primarily in the Sacramento Valley.

Photo © Gary Nafis