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Animal Fact Sheets

Range Map

garter snake range map


 (Thamnophis sirtalis tetrataenia)


Classification and Range

The San Francisco garter snake is a subspecies of the common garter snake Thamnophis sirtalis. It is a strikingly beautiful snake, with dramatic blue, black and red stripes running down the length of the body. Garter snakes belong to the family Colubridae, the largest family of snakes, which includes most of the non-venomous snakes. Common garter snakes range over most of the United States and southern Canada except for most of the Great Plains and the deserts of the Southwest. In fact, they are the most widely distributed North American snake. San Francisco garter snakes are only found on the San Francisco peninsula in about 20 localities, including the Ano Nuevo State Reserve, the San Francisco State Fish and Game Refuge, and the Pescadero Marsh Natural Reserve.


Common garter snakes, including San Francisco garter snakes, are usually found near moist vegetation, often in or near wetlands, along creeks and sloughs, on farms, in moist meadows and near irrigation and drainage ditches.

Length and Weight

Common garter snakes, including the San Francisco garter snake, range in length from 18-51 inches (46-131 cm). A typical size female weighs about 8 ounces (227 gr). Males are much smaller than females, and usually weigh less than half as much.

Life Span

8-15 years (estimate)


In the wild: Amphibians (including tadpoles), earthworms, small fish.

At the zoo: Fish, earthworms.


In the colder parts of their range, male common garter snakes emerge from hibernation first, so they can be ready for females when they appear. Female snakes who have follicles ready for fertilization emit a powerful pheromonal attractant. Groups of males may form a mass around a female, each of the eager little suitors hoping to be the one to actually mate with the larger snake. One or more may manage to insert one of his hemipenes (copulatory organs) into the cloaca of the female and introduce semen into her reproductive tract. Three to four months later, a litter of as many as 85 babies is produced.

Life Cycle

Each newborn snake is only 5 to 9 inches (13-23 cm) long. They immediately disperse and begin a life of hiding from predators while seeking prey even smaller than themselves. Large litters are an indication of how difficult it is for a baby garter snake to survive to adulthood. Many become food for frogs and birds. If they are capable and fortunate, they mature at about 2 years of age.

Grab and Swallow

Garter snakes often detect frogs or tadpoles by sensing their movements in the water along the snake's body. The garter snake then turns and lunges at the source of the sensation and often manages to grab something good to eat as a result. They do not constrict their prey; they simply seize it in their jaws and begin swallowing it alive. Many of the animals they hunt are very easy to swallow — moist and smooth, and shaped well for going down their throats. Frogs and toads try to kick their way out of the snake's mouth, while the garter snake tries to use its small but numerous teeth to prevent its dinner from escaping.

Location at the Zoo

The zoo does not currently have a San Francisco garter snake. However, other species of native (U.S.) reptiles which can be seen in the Day Exhibit are: Louisiana pine snake, desert rosy boa, corn snake and Gila monster, as well as different kinds of rattlesnakes: the northern blacktail and Washington state's only dangerously venomous snake, the Northern Pacific rattlesnake.

Conservation Connection

San Francisco garter snakes are an endangered species. They are also protected by the state of California. San Francisco garter snakes in captivity are only found in zoos, and are on loan from the U.S. Fish and Wildlife Service. Any of these snakes found in private hands are deemed to be illegally collected and those possessing them are prosecuted aggressively. Other dangers the species face include: pollution, wetland development and introduced predators such as bullfrogs.

How You Can Help!

The effort to save endangered species like the San Francisco garter snake requires cooperation and support at the international, national, regional and individual levels. You can help in this cause. Join and become active in Woodland Park Zoo and other conservation organizations of your choice. Don’t buy wild-caught reptiles and other animals for pets. Contact your elected representatives and express your views about conservation of endangered species and wild habitats.

Contact Woodland Park Zoo at to find out other ways you can support conservation programs at the zoo. Discover more about snakes by contacting the Society for the Study of Amphibians and Reptiles at 303 W. 39th St., PO Box 626, Hays, KS 67601. Learn other ways you can help conserve wildlife and the habitats they require for survival by visiting our How You Can Help page.

Reptiles as Pets

We do not recommend reptiles as pets for most people as they require very specialized diets and environments. We also receive hundreds of requests each year to take former pet iguanas, boas and other reptiles but we cannot accept these due to space, health and unknown backgrounds. If you need to find a reptile or amphibian a new home, we suggest you contact a local herpetological group in your area. In the Puget Sound region, contact the Pacific Northwest Herpetological Society as a resource. If you do choose to get a reptile as a pet, please learn as much as possible about their care and the best species before making your decision and never accept wild-caught animals as pets or release non-native reptiles or amphibians into the wild.

Sources and Suggested Reading

Mehrtens, John M. 1987. Living Snakes of the World. Sterling, New York, NY. 480 p.

Nussbaum, Brodie & Storm. 1983. Amphibians & Reptiles of the Pacific Northwest. University Press of Idaho, Moscow, ID. 332 p.

Robert C. 1985. Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston, MA. 336 p.

For Kids!

Markle, Sandra. 1995. Outside and Inside Snakes. MacMillian Books, New York, NY. 40 p.

Resmick, Jane P. 1996. Eyes on Nature: Snakes. Kidsbooks, Inc., Chicago, IL. 29 p.

Zoobooks. 1992. Snakes. Wildlife Education, Ltd., San Diego, CA. 16 p.

Garter Snake Taxonomy

Phylum: Chordata
Family: Colubridae
Species:T. sirtalis tetrataenia

Garter Snake Fascinating Facts

  • This snake is often called the "gardener snake" by those who have misheard the name "garter" and who understand that some kinds of garter snakes help control garden slugs. The garter snake was named due to its resemblance to a garter, an item of clothing not much used these days.
  • San Francisco garter snakes appeared on one of a series of stamps issued by the U.S. Postal Service in October 1996. The stamps featured 15 different U.S. endangered species in order to promote awareness of beleaguered animals.
  • To defend themselves against predators, garter snakes make themselves smell and taste bad. They do this by secreting a powerful musk along with their feces.