SpeU.S . Fish and Wildlife Service

Giant Garter Snake

Thamnophis gigas

2) emergent, herbaceous wetland Wildlife Areas. Historically the giant vegetation, such as cattails and garter snake inhabited the southern bulrushes, for escape cover and Central Valley; however, here have foraging habitat during the active been only a few recent sightings of season; 3) grassy banks and giant garter snakes in the San openings in waterside vegetation for Joaquin Valley. basking; and 4) higher elevation uplands for cover and refuge from Giant garter snakes are typically flood waters during the snake's absent from larger rivers because of inactive season in the winter. the lack of suitable habitat and emergent vegetative cover, and from The giant garter snake inhabits small wetlands with sand, gravel, or rock CLASSIFICATION mammal burrows and other soil substrates. While not always the Threatened—October 1993 crevices above prevailing flood case, riparian woodlands typically do elevations throughout its winter not provide suitable habitat because DESCRIPTION inactive period. They typically select of excessive shade, lack of basking The giant garter snake is one of the burrows with sunny exposure along sites, and absence of prey largest garter snakes, with females south and west-facing slopes. The populations. reaching an average length of about breeding season extends through 34 inches in the San Joaquin Valley. March and April, and females give THREATS Females tend to be slightly longer birth to live young from late July Habitat loss and fragmentation, flood and proportionately heavier than through early September. control activities, changes in males. Female giant garter snakes agricultural and land management typically weigh 1-1.5 pounds. Giant Brood size is variable, ranging from practices, predation from introduced garter snakes are in the family 10 to 46 young, with an average of species, road mortalities, and water Colubridae, which includes most of 23. The young snakes immediately pollution are the main causes for the the species of snakes found in the scatter into dense cover and absorb decline of this species. western United States. their yolk sacs, after which they hunt independently. Although growth Giant garter snakes can inhabit water The basic color on the snake's back rates are variable, young typically bodies that contain predatory fish. varies from brownish to olive with a more than double in size within the When lots of cover is available, they checkered pattern of black spots, first year. Sexual maturity averages 3 seem to hold their own, even when separated by a yellow dorsal stripe years for males and 5 years for numerous predators share the same and two light colored lateral stripes. females. habitats. Giant garter snakes are Background coloration and probably absent from larger rivers prominence of a black checkered DISTRIBUTION because the habitat is not suitable, pattern and the three light stripes are The giant garter snake inhabits not because of the fish. The major geographically and individually agricultural wetlands and other rivers have been highly channelized, variable. The snake's underside is waterways such as irrigation and removing oxbows and backwater cream to olive or brown and drainage canals, sloughs, ponds, areas that probably at one time sometimes infused with orange, small lakes, low gradient streams, provided suitable habitat. especially in northern populations. and adjacent uplands in the California Central Valley. Due to the CRITICAL HABITAT: Giant garter snakes feed primarily on direct loss of natural habitat, the None small fish, tadpoles, and frogs. giant garter snake relies heavily on Habitat requirements consist of: 1) rice fields in the Sacramento Valley, RECOVERY PLAN: adequate water during the snake's but also uses managed marsh areas None active season (early-spring through in Federal National Wildlife Refuges mid-fall) to provide food and cover; and State

September 2016