Giant Garter Snake

Photo credits: Sutter Basin Conservation Bank, Westervelt Geological Services

Kids' Species Information

Giant Garter Snake

STATUS

Threatened. That means we are concerned about the species but that they are not in danger of extinction right now.

DESCRIPTION

The giant garter snake is one of the largest garter snakes. They are at least 162 centimeters long. (About 64 inches.)

Females tend to be longer and heavier than males. They weigh 500 to 700 grams. (About 1 to 1.5 pounds)

The back of a giant garter snake varies from brownish to olive. There is a checkered pattern of black spots. A yellow stripe runs down the center of the back. Along the sides are light colored stripes. The underside is cream to olive or brown. Sometimes it is orangish.

Look at this picture (left) of the common garter snake. Notice the red spots. Giant garter snakes don't have these. And common garter snakes are only 46-140 cm long. Otherwise, the two species look very similar.

Garter snakes are not dangerous. In California, only rattlesnakes have venom that is dangerous to humans.

FOOD

Small fishes, tadpoles and frogs.

HABITAT

Agricultural wetlands and other waterways in the Central Valley. (Irrigation and drainage canals, sloughs, ponds, small lakes, streams.)

Most of the natural habitat has been lost. So lots of snakes live in rice fields. Rice fields provide hundreds of thousands of acres of habitat for the species. See a California Rice Commission web page on how species use the fields.

Habitat needs

Enough water to provide food and cover during the active season. (Early-spring through mid-fall) Wetland plants such as cattails and bulrushes. (These are for cover and foraging.) Grassy banks and openings in vegetation for sunning.

Winter refuges: Small mammal burrows and other crevices above flood elevations. Giant garter snakes are dormant during the winter so they need places like this to hang out.

SEASONAL LIFE CYCLE

Giant garter snakes are most active from early spring through mid-fall. Between April 1 and May 1, they emerge and start hunting for food. Around October 1, they start looking for winter retreats. By November 1, they are in winter retreats and mostly stay there until spring. Some may bask or move short distances on warmer days.

MATING

Males reach sexual maturity in three years, females in five. The breeding season extends through March and April. Females give birth to live young from late July through early September.

young giant garter snake

Photo: Adam Zerrenner, USFWS

Brood size varies. It ranges from 10 to 46 young. (See photo of young snake, left) Young immediately scatter into dense cover. They typically more than double in size in the first year.

PREDATORS

These include raccoons, skunks, opossums ("possums"), foxes, hawks, northern harriers, egrets, bitterns and great blue herons.

Bullfrogs. These are not native to this area. They prey on young garter snakes. See report. (47 KB PDF)

RANGE

Mainly the Sacramento Valley of California. Some isolated populations in the San Joaquin Valley.

THREATS

Habitat loss and fragmentation. Flood control activities. Changes in agricultural and land management practices. Predation from introduced species, parasites, water pollution.

EXPLORE

Learn more about snakes. Visit a local zoo or nature center. If you are lucky enough to see a giant garter snake, just look, don't touch.

MORE READING

CaliforniaHerps.com has lots of information about snakes, lizards, frogs, turtles and salamanders. See their species account about the giant garter snake. Please note: This is not a Fish & Wildlife Service web site.

Lavies, Bianca. 1993. A Gathering of Garter Snakes. Dutton. A book about red-sided garter snakes in Manitoba, Canada for kids 9-12.

Montgomery, Sy. 1999. The Snake Scientist. Houghton Mifflin. Another book about red-sided garter snakes in Manitoba, Canada for kids 9-12.

Thelander, Carl. ed. 1994. Life on the edge: a guide to California's endangered natural resources. BioSystem Books. Santa Cruz, CA. p 284-287.

See What You Can Do to Help Wildlife and Plants (201 KB PDF) for ideas about how to help threatened and endangered species.

Words to Learn

Biologists who study snakes, frogs, turtles, salamanders and other reptiles and amphibians are called herpetologists.

Herpetologists call giant garter snakes Thamnophis gigas. Scientific names are in Latin or Greek.

Thamnophis means "bush snake." Gigas means "giant."

Garter snakes are in the Colubridae family. This includes most of the species of snakes found in the western United States.

Giant garter snakes are mainly active during the daytime. Scientists say they are diurnal. Animals who are active at night are called nocturnal. Giant garter snakes are sometimes active on warm evenings.