The San Francisco garter snake (Thamnophis sirtalis tetrataenia) is a slender multi-colored subspecies of the common garter snake. Designated as an endangered subspecies since the year 1967, it is endemic to San Mateo County and the extreme northern part of coastal Santa Cruz County in California. Adult San Francisco garter snakes can grow to a total length of 18 - 55 inches (46 – 140 cm). They have keeled dorsal scales of blue-green, bordered by stripes of black, red (sometimes orange), and blue-green. Their head is barely wider than the neck, and is red. Its eyes are large compared to other species of garter snakes, giving the snake good eyesight to be primarily active during the day. Studies have shown that snout length is indicative of reproductive behaviors, as great snout length is correlated with ovarian follicle growth, which increases sexual activity of the female subspecies. Garter snakes are practically harmless to humans. Their bites are fatal to their prey, but only cause a mild irritation for humans. With mildly toxic venom in their saliva, garter snakes possess no fangs. (Source: Wikipedia.org, CC BY-SA)