Thamnophis couchii

Sierra Garter Snake

Family: Colubridae · Class: Reptilia · Order: Squamata

The Sierra Garter Snake (Thamnophis couchii), also known as Couch's Garter Snake, is a medium-sized, semi-aquatic snake species native to western North America. Adults typically measure 45 to 75 cm (18 to 30 inches) in total length, with some individuals reaching up to 91 cm (36 inches). The species exhibits considerable color variation, generally displaying a olive-brown to grayish-brown dorsal coloration with three longitudinal stripes. The middorsal stripe is typically cream, yellow, or orange, while the lateral stripes are lighter colored and positioned on the second and third scale rows. The underside is pale yellow to cream with dark markings along the edges of the ventral scales. Sierra Garter Snakes occur throughout much of California, extending from the Sierra Nevada foothills and Central Valley into the Coast Ranges, and north into Oregon and Washington. In California, they are found from sea level to elevations exceeding 2,400 meters (7,900 feet) in mountainous regions. The species has a relatively broad distribution within the state, occupying diverse geographic regions including the northern Sierra Nevada, southern Cascade Range, and portions of the Coast Ranges. This species inhabits a variety of aquatic and semi-aquatic environments, showing strong association with permanent or semi-permanent water sources. Sierra Garter Snakes are commonly found near streams, creeks, ponds, lakes, marshes, and wet meadows. They prefer areas with dense vegetation along water margins that provide cover and hunting opportunities. The species also utilizes artificial water sources including irrigation canals, stock ponds, and urban water features. Adjacent upland areas are important for thermoregulation and overwintering habitat. Sierra Garter Snakes are opportunistic predators with a diet consisting primarily of amphibians, fish, and aquatic invertebrates. They feed heavily on frogs, toads, tadpoles, salamanders, and small fish, supplemented by earthworms, slugs, and occasionally small rodents or birds. The species is ovoviviparous, with mating occurring in spring following emergence from winter dormancy. Females give birth to live young in late summer, with litter sizes ranging from 4 to 19 offspring. Young snakes are approximately 15 to 20 cm (6 to 8 inches) at birth and reach sexual maturity in 2 to 3 years. Currently, Thamnophis couchii does not hold federal or state listing status in California. According to NatureServe, the species is represented by numerous occurrences across its range, with some populations occurring within protected areas. However, like many aquatic-dependent species, Sierra Garter Snakes face potential threats from habitat modification, water diversions, pollution, and introduced predators such as bullfrogs and predatory fish. Climate change may pose additional challenges through altered precipitation patterns and reduced snowpack affecting stream flows. Conservation of riparian habitats and maintenance of adequate water levels in aquatic systems remain important for the species' long-term viability.

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, and more.