Thamnophis sirtalis tetrataenia

San Francisco gartersnake

(c) Guillermo Roque, some rights reserved (CC BY) · licence

Family: Colubridae · Class: Reptilia · Order: Squamata

Conservation status: FP · Endangered · G5T2Q S2

Thamnophis sirtalis tetrataenia (San Francisco gartersnake) is a California animal in the Colubridae family.

The San Francisco gartersnake is a slender, colorful subspecies of the common gartersnake distinguished by its distinctive coloration pattern. Adults can reach lengths of 3 feet (0.9 meters) or more, with a burnt orange head and a greenish-yellow dorsal stripe edged in black. This central stripe is bordered by red stripes that may be continuous or broken with black blotches, followed by black lateral stripes. The belly varies from greenish-blue to blue, creating a striking ventral appearance that aids in field identification. This subspecies is endemic to the San Francisco Peninsula, with its current range restricted primarily to San Mateo County, California. Historically, the species occurred more widely throughout the San Francisco Bay area, but habitat loss has significantly reduced its distribution. The largest known populations occur at Pescadero Marsh Natural Preserve in coastal San Mateo County, with smaller populations persisting in fragmented habitats throughout the region. San Francisco gartersnakes require both aquatic and terrestrial habitats for their survival. They are typically found in or adjacent to freshwater aquatic environments, including ponds, creeks, marshes, and seasonal wetlands. The species utilizes upland areas for basking, shelter, and overwintering, often in grasslands, coastal scrub, and woodland edges. This dual habitat requirement makes the species particularly vulnerable to habitat fragmentation, as individuals must move between aquatic breeding areas and terrestrial refugia. As semi-aquatic predators, San Francisco gartersnakes feed primarily on amphibians, particularly frogs and their larvae, as well as fish, earthworms, and occasionally small mammals. The species is closely associated with populations of native amphibians, especially the California red-legged frog, which serves as a primary prey species. Mating typically occurs in spring following emergence from winter dormancy, with females giving birth to live young in late summer. Like other gartersnakes, this subspecies is ovoviviparous, retaining eggs internally until hatching. The San Francisco gartersnake was listed as endangered under the federal Endangered Species Act and is also listed as endangered by the State of California with full protection status. The species faces severe threats from urban development, habitat fragmentation, and wetland destruction throughout the San Francisco Peninsula. According to USFWS documentation, primary threats include residential and commercial development, road construction, golf course development, and agricultural conversion. The species' dependence on both aquatic and upland habitats makes it particularly susceptible to development pressures that fragment these connected ecosystems. Water management practices that alter natural hydrology and the introduction of non-native predators and competitors further threaten remaining populations. Recovery efforts focus on habitat protection, restoration of degraded wetlands, and maintenance of wildlife corridors connecting fragmented habitat patches. The species' limited range and ongoing development pressure in the San Francisco Bay area continue to pose significant challenges to long-term recovery.

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