Crotalus cerastes

The sidewinder (Crotalus cerastes), also known as the horned rattlesnake and sidewinder rattlesnake, is a venomous pit viper species belonging to the genus Crotalus (rattlesnakes) and is found in the desert regions of the southwestern United States and northwestern Mexico. Three subspecies are currently recognized, including the nominate subspecies described here. A small species, adult specimens measure between 43 and 76 cm (17 and 30 in) in length. Most adults are 50–80 cm (19.5–31.5 in) in length. The females are larger than the males, which is unusual for this group of snakes. Usually, 21 rows of keeled dorsal scales occur midbody. Males have 141 or fewer ventral scales; females have 144 or fewer. It is sometimes referred to as the horned rattlesnake because of the raised supraocular scales above its eyes. This adaptation may help shade the eyes or prevent sand drifting over them as the snake lies almost buried in it. The color pattern consists of a ground color that may be cream, buff, yellowish-brown, pink, or ash gray, overlaid with 28-47 dorsal blotches subrhombic or subelliptical in shape. In the nominate subspecies, the belly is white and the proximal lobe of the rattle is brown in adults. Klauber and Neill describe the ability of this species to display different coloration depending on the temperature—a process known as metachrosis. Sidewinder, horned rattlesnake, sidewinder rattlesnake, Mojave Desert sidewinder (for C. c. cerastes), sidewinder rattler. In the southwestern United States, this species is found in the desert region of south eastern California, southern Nevada, southwestern Utah, and western Arizona. In northwestern Mexico, it is found in western Sonora and eastern Baja California. This species is classified as Least Concern on the IUCN Red List (v3.1, 2001). Species are listed as such due to their wide distribution, presumed large population, or because they are unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend was stable when assessed in 2007. The common name sidewinder alludes to its unusual form of locomotion, which is thought to give it traction on windblown desert sand, but this peculiar locomotor specialization is used on any substrate over which the sidewinder can move rapidly. As its body progresses over loose sand, it forms a letter J-shaped impression, with the tip of the hook pointing in the direction of travel. Sidewinding is also the primary mode of locomotion in other desert sand dwellers, such as the horned adder (Bitis caudalis) and Peringuey's adder (Bitis peringueyi), but many other snakes can assume this form of locomotion when on slick substrates (e.g., mud flats). Sidewinder rattlesnakes can use sidewinding to ascend sandy slopes by increasing the portion of the body in contact with the sand to match the reduced yielding force of the inclined sand, allowing them to ascend up to the maximum possible sand slope without slip. Implementing this control scheme in a Snakebot capable of sidewinding allowed the robot to replicate the success of the snakes.