Giant Garter Snake

The giant garter snake (Thamnophis gigas) is the largest species of garter snake. Relatively rare, it is a semi-aquatic snake with a limited distribution in the wetlands of central California.

Description

The giant garter snake is the largest species of garter snake, with the adult snakes ranging from 94–165 cm (37.0–65.0 in) in length. As with many snakes, the female giant garter snakes tend to be longer and larger than the males. The snakes have keeled scales, with a yellow dorsal stripe against two additional yellow stripes on either side that run the length of its body. Although, some unstriped checkered patterns have been observed. It is venomous, but harmless to humans; it possesses a very mild neurotoxic venom that helps subdue its prey. A bite to a human will at most give a red itchy rash around the area of the bite.

Distribution

The giant garter snake is found in Central California. Its historic range extends through much of Central California's Sacramento and San Joaquin valleys but has been reduced to a few fragmented areas in the Sacramento Valley. Due to its semiaquatic nature, it is rarely found more than a few meters from water during the active season. This reliance on water has prevented the giant garter snake from dispersing to new habitats effectively and is also responsible for fragmenting populations of the snake, as the areas between habitats are often inhospitable for it. Because of this, giant garter snakes are typically found in areas that they inhabited previously, even if those areas were destroyed or converted. The snake historically inhabited wetland habitats, particularly tule marshes, but due to the destruction of these habitats, it is now predominantly found in artificial wetlands associated with rice agriculture.

Giant garter snakes prefer to inhabit stagnant or slow-moving water bodies with emergent vegetation; they use water to thermoregulate and deep and fast-moving water bodies are too cold, while emergent vegetation protects them from predators. Despite their dependence on water, giant garter snakes spend most of their time on land during the active season and all their time in brumation on land during the winter. They spend most of their time on land underground. When not underground, they seek litter or vegetation (particularly tules) to use as cover from predators and environmental extremes, and they avoid rocky or otherwise open areas. Giant garter snakes associated with rice agriculture use rice field canals during the spring and autumn and use rice fields throughout the active season, as they provide good habitat for the snakes with plentiful food, water, and cover. Due to habitat destruction, most giant garter snakes live in rice agricultural wetlands, and thus most live on private property, which provides a barrier to their study and conservation.

Behaviour and ecology