Facts, Identification & Control

Latin Name

Thanophis gigas


The giant garter snake is one of the largest North American snakes. Its scaly skin has many color variations – from brown to olive to black – and can sometimes have yellowish stripes or a checkered pattern. Its head is slightly wider than the neck. Snakes at the northern end of the range show distinct stripes. Giant garter snakes in the San Joaquin Valley may also have indistinct stripes or no stripes with an underside of light brown or light gray. This is the largest species of garter snake. While adults may be up to 65 inches long, most are about 36 – 48 inches in length.

Behavior, Diet & Habits

The giant garter snake is found only in California and has historically ranged from Kern County north along the Central Valley to Butte County, with a gap in the central part of Glenn County to the southern edge of the San Francisco Bay delta, and from Merced County to northern Fresno County. Its natural habitat is aquatic habitats such as marshes, sloughs, drainage canals and irrigation ditches, especially around rice fields, and other managed wetlands that are periodically flooded by human action rather than the natural flooding. The giant garter is active during the day, and at night in hot weather. Secretive and difficult to approach, this snake will quickly dive to the bottom of the water before giving a predator or casual observer the opportunity to get a close look. This behavior probably derives from the habitat of this snake, which is often shared with many airborne predators such as egrets, herons and hawks. Adult snakes emerge from overwintering sites in March, and warm themselves by resting on vegetation near water in spring. They stay active until the fall and overwinter in abandoned animal burrows. It feeds primarily on fish, frogs, tadpoles earthworms, leeches, ants, frogs and rodents that it can overpower.

Mating takes place soon after emergence in the spring. Females bear live young from July through early September. When threatened or picked up, this snake will excrete a foul-smelling musk

More Information

The giant garter snake is identified as “threatened” by the State of California and the U.S. Fish and Wildlife Service, the result of widespread destruction of wetland habitat. The giant garter snake populations of the San Joaquin Valley are now tiny, disconnected remnants of its former range. However, this snake has fared better in the Sacramento Valley because rice cultivation and the associated agricultural canals have provided it with an acceptable habitat. In addition to habitat loss and fragmentation, introduced predators such as the American bullfrog may also limit populations. Fortunately, though threatened, the snake is listed as a “high recovery potential” species and with good maintenance of state and federal wetlands, the giant garter snake population can bounce back.

When snakes are a problem, the best course of action is to call a pest management professional (PMP) who has the tools and knowledge to address snake problems. In addition, snakes enter areas inhabited by people in search of food and shelter. The easiest thing you can do to help prevent a snake encounter is to make your home and yard less appealing to them.