Hypsiglena torquata is a species of rear-fanged, colubrid snake known as the night snake. They are found through the south and western United States, as well as Mexico. The number of subspecies varies depending on the source, but it is generally accepted that there are 17.
- Boulenger's Night Snake Hypsiglena torquata affinis Boulenger, 1894
- Cedros Island Night Snake, Hypsiglena torquata baueri (Zweifel, 1958)
- Santa Catalina Night Snake, Hypsiglena torquata catalinae (Tanner, 1966)
- Sonoran Night Snake, Hypsiglena torquata chlorophaea (Cope, 1860)
- Desert Night Snake, Hypsiglena torquata deserticola (Tanner, 1966)
- Isla Partida Night Snake, Hypsiglena torquata gularis (Tanner, 1954)
- Texas Night Snake, Hypsiglena torquata jani (Dugès, 1866)
- San Diego Night Snake, Hypsiglena torquata klauberi (Tanner, 1944)
- Mesa Verde Night Snake, Hypsiglena torquata loreala (Tanner, 1944)
- San Martin Island Night Snake, Hypsiglena torquata martinensis (Tanner & Banta 1962)
- California Night Snake, Hypsiglena torquata nuchalata (Tanner, 1943)
- Spotted Night Snake, Hypsiglena torquata ochrorhyncha (Cope, 1860)
- Tiburon Island Night Snake, Hypsiglena torquata tiburonensis (Tanner, 1981)
- Collared Night Snake Hypsiglena torquata torquata (Günther, 1860)
- Isla Tortuga Night Snake Hypsiglena torquata tortugensis (Tanner, 1944)
- Clarion Island Night Snake Hypsiglena torquata unaocularis (Tanner, 1944)
- Central Baja Night Snake, Hypsiglena torquata venusta (Mocquard, 1899)
Length is 12–26 in (30–66 cm). Pale grey, light brown, or beige in color with dark grey or brown blotches on the back and sides. The nightsnake's head is rather flat and triangular shaped and usually has a pair of dark brown blotches on the neck. It is often mistaken as a juvenile rattlesnake, however the nightsnake's lack of rattles is an easy way to differentiate. Rattlesnakes are, however, born without a rattle. The nightsnake also has a black or dark brown bar behind the eyes that contrast against the white or pale grey upper labial scales. The belly of the nightsnake is white or yellowish and it also has a vertical pupil.
The nightsnake has been found as far north as southern British Columbia, and as far south as Guerrero, Mexico. The Eastern range of the night snake extends to Texas. Still, not much is known as far as population densities and exact range due to the highly cryptic nature of the night snake.
The nightsnake is found in many differing types of habitat including: grasslands, deserts, sagebrush flats, chapparral, woodlands, thornscrub, thorn forest, and mountain meadows. Both rocky and sandy areas are inhabited by night snakes and elevations over 8,000 ft have been recorded. The night snake is also known to inhabit mammal burrows.
Night snakes are known to be both crepuscular (most active at dawn and dusk), and nocturnal. Night snakes are usually seen at night while crossing roads, but can be found under rocks, boards, dead branches and other surface litter during the day. Although the night snake poses no threat to humans, it is slightly venomous and uses this venom to subdue its prey. Their main prey is lizards, a study in southwestern Idaho found that the night snakes diet consisted mostly of side-blotched lizards (Uta stansburiana) and their eggs. Other prey includes juvenile rattle snakes and blind snakes, salamanders, frogs, and large insects. Night snakes hibernate during the winter months and are known to aestivate during periods of the summer. They are generally most active from April to October, with peaks of activity usually occurring in June. Night snakes are known to be docile and easily handled. If threatened, the night snake may coil up and thrust its coils at the threat while flattening its head into a triangular defensive shape. Female night snakes are usually longer and larger than males.
Night snakes mate in the spring and females lay a clutch of 2–9 eggs from April to August. Eggs hatch in 7 to 8 weeks, usually late summer. Males reach sexual maturity after one year, captive night snakes have lived over 12 years.