Nightsnake

A small (up to 23"), gray or tan snake with dark, brownish-gray blotches. The row of blotches on the back is usually single, although displacement along the midline often gives the impression of two rows of offset blotches. A dark "collar" on the neck consists of one, two, or three blotches. It has vertical pupils and a pale belly with no markings. This crepuscular and nocturnal snake (hence the name "nightsnake") is regularly encountered by driving roads at night. Primarily consumes lizards, snakes and their eggs, but also frogs, toads, insects, and possibly scorpions. Its venom produces severe, often fatal hemorrhaging in snakes, but has minimal effect on mammals. Harmless to humans. (from "A Field Guide to Amphibians and Reptiles in Arizona")