Thamnophis sirtalis infernalis - California Red-sided 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.
Ground color is dark olive to black. The dorsal stripe is wide and well-defined, and yellowish to bluish in color. Light stripes along the lower sides are not very distinct, often blending in with the color of the belly. There are red bars alternating with the ground color along the sides above the lateral stripes. The head is red or orangish. The underside is bluish gray, sometimes very blue north of the Bay Area (shown above) and may have some dark coloring. The eyes 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, 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 infernalis - California Red-sided Gartersnake, is endemic to California, ranging from Humboldt County south, along the coast ranges (excluding much of the San Francisco peninsula) and east of the San Francisco Bay to just below the Monterey Bay where T. s. fitchi takes over. Continues from where T. s. fitchi drops out in Santa Barbara county south along the coast to San Diego County. (Snakes from the Santa Clara River area in Ventura County south, may prove to be a new species [Stebbins]).

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.

We are following Rossman et al. for the range of T. sirtalis along the central coast. Stebbins and others show the range of T. s. infernalis continuing south of Monterey Bay through the coast ranges south of the Bay Area to San Diego County. Here is an alternate map showing this distribution.

Habitat

Utilizes a wide variety of habitats - forests, mixed woodlands, grassland, chaparral, farmlands, often near ponds, marshes, or streams. 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.

The South Coast Gartersnake

Southern California Common Garter Snakes have been treated as a unique taxon - Thamnophis sirtalis ssp. - South Coast Gartersnake, but the recognition of this subspecies is rare. The only published description I can find is in the following paper:
Jennings, Mark R. and Marc P. Hayes. Amphibian and Reptile Species of Special Concern in California. California Department of Fish and Game, published November 1, 1994.

The information about this snake that was published in the paper can be found on the California Dept. of Fish and Game website.

Jennings and Hayes state that this snake is known from scattered localities from the Santa Clara River Valley in Ventura County south to the vicinity of San Pasqual in San Diego County. It is restricted to marsh and upland habitats near permanent water with good strips of riparian vegetation where adequate prey and refuge can be found. Conservation Issues (Conservation Status) None for the northern population.

The California Department of Fish and Game lists the South Coast Gartersnake as a California Species of Special Concern. Jennings and Hayes (in the 1994 paper cited above) state that 75 percent of the known historic localities for this snake no longer support snakes due to habitat loss from urbanization and flood control projects, floods, extended droughts, and introduced aquatic predators.