Description
Considered among the smallest rattlesnakes in California, this species has a moderately-bodied pit viper with keeled scales, elliptical eyes, spade-shaped head, infrared pits on either side of the head between their eye and nostril, and a distinctive rattle at the tip of its tail. Also commonly called the “horned rattlesnake” due to the scales over the eyes – termed supraocular scales – that are enlarged and raised, giving the appearance of horns. These scales act as protection by folding down over the eyes when snakes are burrowing into the sand and loose soils. Coloration is highly variable and regulated with changes in temperature. Dorsal coloration ranges from pale cream, grayish, tan, and brown to pink. Ventrally white in color. Patterns consist of dark elongated diamond blotches on the dorsal surface. A dark stripe extends from the eyes back toward the upper corner of the jaw. The most noticeable difference among the two subspecies is the color of the bottom segment of its rattle. The Colorado Desert Sidewinder has a black basal rattle segment, while the Mojave Desert Sidewinder has a brown segment. Adult lengths range from 17-33 inches, generally staying within 12-18 inches. Adult females are larger than males.

Habitat
Confined to southeast and south central California, south and east of the Sierra Mountains. Inhabits primarily open deserts, wind-blown sandy areas such as the sandy flats in creosote and mesquite deserts where sand hummocks are topped with vegetation, thickly vegetated sandy washes, hardpan flats, rocky hillsides, and other desert areas.

Diet
Primarily eats lizards, especially when young. Also preys on small mammals, pocket mice, kangaroo rats, small birds, and small snakes. As ambush hunters, the adult snake awaits coiled in a self-constructed depression known as cratering, in areas trafficked by prey. When prey passes, it strikes, releases, and then tracks the prey following the scent trail, where the envenomated animal is consumed whole. Neonates flick their tail to attract lizards (caudal luring), holding onto prey until envenomation has taken effect.

Behavior
Named for its unique sidewinding style of movement, this rattlesnake is typically unaggressive but will act in self-defense if provoked or startled. Heavily keeled scales allow for the sidewinding form of locomotion, throwing raised loops of the body, traversing laterally in an S-shaped curve leaving signature J-shaped depressions in the sand. Primarily crepuscular – most active during dusk or dawn – when the temperatures are moderate to cool. During periods of excessive heat, they hide in tortoise and rodent burrows or stay almost fully submerged in the sand; a behavior called “cratering.”

Reproduction
Mating occurs in the spring with a secondary peak in the fall. Females will give birth to 2-18 live young (ovoviviparous) born between July and September following a 121-151 day gestation period. Neonates measure approximately 7 inches at birth and are born with a single button at the end of the tail that doesn’t produce the rattle sound until additional segments are added during successive shedding. Females will protect the neonates for 7-10 days, after which the first shedding occurs and the young leave the burrow. They become sexually mature at 3 years.

Venom Profile
Venom is less toxic than other rattlesnakes and a lower quantity is injected upon envenomation. Venom consists of hemotoxins and neurotoxins. Hemotoxins target red blood cells and the circulatory system by interfering with blood pressure, platelets and clotting factors. Neurotoxins can cause paralysis, weakness, respiratory failure and muscular twitching. Antivenin treatment may require multiple doses over several days to neutralize the venom, which may cause permanent damage and disfigurement even when administered shortly after envenomation.

Range
Colorado Desert Sidewinder – Imperial, Riverside, San Bernardino*, and San Diego counties.

Mojave Desert Sidewinder – Inyo, Kern, Los Angeles, Mono*, Riverside*, and San Bernardino counties.

*Indicates counties where the species’ range extends only into a minor portion of the county.