About Thamnophis atratus Kennicott, 1860
The aquatic garter snake (Thamnophis atratus) reaches an adult length of 18 to 40 inches, or 46 to 102 centimeters. This species has highly variable dorsal coloration. Common color patterns include pale gray with alternating rows of darker blotches on the sides, dark brown with less distinct borders, or nearly solid all black. A long yellow stripe running down the back may be absent, present, confined only to the neck, or very indistinct. The snake's throat and underside range from whitish to yellow. One distinct color morph of this species has a blue-gray base color with a faint olive dorsal stripe and white dots along its sides. A second color morph has a yellow dorsal stripe with black spots along its sides. This second morph has the classic appearance of a typical garter snake, but it is classified as part of this species due to its behavior and scale patterns. This snake is found only along the coasts of Oregon and California. It most commonly occurs along the edges of bushlands, woodlands, grasslands, and forests, located close to ponds, marshes, streams, and lakes. The aquatic garter snake gives birth to live young, with broods containing between three and 12 offspring per litter.
