California red sided garter snake
This subspecies is found in a limited area of the US west coast. It lives close to water, and feeds mainly on amphibians. Its population is believed to be declining due to habitat destruction, and to its main prey item (red-legged frog) becoming scarce, again partly due to habitat destruction, and partly due to the presence of the American bullfrog, which not only competes with the red-legged frog, but also will eat small snakes.
The snakes I have originate from Marin County, which has the most attractive colours. They develop an increasing blueness as they mature – visible on these pictures where the 2-3 month old juvenile in the first picture is compared with the older one in the second picture.
Thamnophis sirtalis infernalis
San Francisco garter snake
The San Francisco garter snake is critically endangered in the wild