True to their name, giant garter snakes (Thamnophis gigas) certainly aren't diminutive, measuring between 36 and 65 inches long. Although they're not yet considered endangered, they're classed as "vulnerable" on the International Union for Conservation of Nature's Red List and are "threatened" according to both federal and California state law. Endemic to California, they're only found between Glenn County and the San Francisco Bay Delta, and from Merced County to northern Fresno County.
Loss of Habitat
As a semi-aquatic species, giant garter snakes have specific habitat needs. They like to live in wetlands, marshes, sloughs, canals, ponds, irrigation ditches and slow-moving creeks. However, they also require ample vegetation and dry land for basking. Sadly, up to 95 percent of this species' natural habitat has been lost, degraded or fragmented to make way for grazing land or development. Flood control, dams and draining of wetlands all degrade this habitat and have a huge impact on these snakes.
Use of agricultural chemicals and pesticides is another threat to giant garter snakes. As the areas they live in are largely surrounded by farmland, runoff from fertilizers and pesticides is a big issue. These chemicals are responsible for killing a large number of the species' natural prey, such as fish, frogs and tadpoles. Without enough food to sustain them, they can't hope to thrive in their native environment.
Introduced species are a danger to giant garter snakes. The introduction of new predators to their environments upsets the local ecosystem and causes more snakes to die. One of the biggest problem species is the bullfrog, which has been introduced into almost every area in which these snakes live, and can consume garter snakes up to 31 inches long. Bass are another problematic predatory species, as are domestic cats and dogs, who have been known to hunt and kill these snakes.
Accidents and Ailments
A variety of accidents and ailments can befall giant garter snakes, reducing their numbers. Road accidents are a fairly large problem, especially in areas where roads are in close proximity to snake populations. Paved roads are more problematic than gravel ones, as vehicles tend to move faster and there's increased traffic. Parasites, such as nematode worms, can also cause mortality in this species. They may also be threatened by other diseases, but little is currently known about this.