Thamnophis sirtalis tetrataenia - San Francisco Gartersnake

Nonvenomous

Gartersnakes have toxins in their saliva which can be deadly to their prey and their bite might produce an unpleasant reaction in humans, but they are not considered dangerous to humans.

Size

Adults of this species measure 18 - 55 inches in length (46 - 140 cm), but the average size is under 36 inches (91 cm).

Appearance

A medium-sized snake with a head barely wider than the neck and keeled dorsal scales. Robert Stebbins calls this snake "One of the most beautiful serpents in North America." A wide blue-green or greenish yellow dorsal stripe is bordered with black stripes. Below the black stripe is a continuous red stripe, bordered below by another black stripe. Below that is a bluish or greenish yellow lateral stripe. There may also be a thin line of black below the lateral stripe on the edge of the belly. The underside is bluish-green. Occasionally, the red stripes may be marked with black, similar to T. s. infernalis. The head is red, with eyes that are relatively larged compared with other gartersnake species.

Behavior

Primarily active during daylight. A good swimmer. Often escapes into water when threatened. When first handled, typical of gartersnakes, this snake often releases cloacal contents and musk, and strikes. The species T. sirtalis is capable of activity at lower temperatures than other species of North American snake.

Diet

Eats a wide variety of prey, including amphibians and their larvae (the endangered California Red-legged Frog - Rana draytonii, is a main food source), fish, birds, and their eggs, small mammals, reptiles, earthworms, slugs, and leeches. This snake is able to eat adult Pacific newts (Taricha) which are deadly poisonous to most predators.

Reproduction

Mating occurs in the spring (and possibly the fall ) and young are born live, spring to fall.

Range

This subspecies, Thamnophis sirtalis tetrataenia - San Francisco Gartersnake, is endemic to California, found only on the San Francisco peninsula from near the southern San Francisco County line south to Ano Nuevo in San Mateo County. (There is also a record from Rancho del Oso state park in Santa Cruz County.)

The species Thamnophis sirtalis - Common Gartersnake, has the largest distribution of any gartersnake, ranging from the east coast to the west coast and north into Canada, farther north than any other species of snake in North America.

Habitat

Utilizes a wide variety of habitats, preferring grasslands or wetlands near ponds, marshes and sloughs. May overwinter in upland areas away from water.

Stebbins (2003) lists the elevation record for the species (not specifically this subspecies) as 8,000 ft. (2,438 m).

Taxonomic Notes

In 1995, Doug Rossman and Jeff Boundy re-named the Thamnophis sirtalis found on the San Francisco Peninsula T. s. infernalis, (removing the name T. s. tetrataenia, but recognizing that the snakes were still subspecifically distinct), and lumped the coastal T. sirtalis with T. s. concinnus. This taxonomy is shown on the range map in the 1996 book, The Garter Snakes - Evolution and Ecology 1. In 1998, Sean Barry and Mark Jennings petitioned the International Commission on Zoological Nomenclature (ICZN) to restore the previous nomenclature 2. With no opposition from Boundy or Rossman, the ICZN agreed to restore the name T. s. tetrataenia to snakes on the San Francisco peninsula 3. Nevertheless, some authors either missed the restoration of this nomenclature or chose to ignore it, and their work still reflects Rossman and Boundy's nomenclature.

(Thanks to Sean Barry for this clarification) Conservation Issues (Conservation Status) Listed as endangered by the state and by the federal government. The habitat of this snake has declined severely due to urban development and agricultural land use and altering of the waterways needed by this snake. These habitat changes have also reduced populations of one of this snake's main food sources, the California Red-legged Frog - Rana draytonii . Some authorities believe that the remaining fragmented populations of this snake could be further threatened by overcollecting for the pet trade. San Francisco Gartersnakes are popular pets in Europe, where it is possible that there are more of these snakes than there are in the wild in California.