Sidewinder

About the sidewinder

The sidewinder, also known as the horned rattlesnake or sidewinder rattlesnake, is a species of pit viper native to desert regions of the southwestern United States and adjacent northwestern Mexico. It belongs to the subfamily Crotalinae within the viper family Viperidae, and three subspecies are recognized. It is a small species: adults measure between 17 and 31.5 inches in total length, and unusually for a U.S. rattlesnake, females run larger than males.

The sidewinder typically has 21 rows of keeled scales at midbody, with males carrying 141 or fewer ventral scales and females 144 or fewer. Its common name "horned rattlesnake" comes from the raised, horn-like scales above each eye, which likely shade the eyes and keep drifting sand out as the snake lies partly buried; because pressure on top of the horns folds them down, researchers believe they also protect the eyes when the snake strikes into rodent burrows. Its background color ranges from cream, buff, and yellowish-brown to pink or ash gray, overlaid with 28 to 47 dorsal blotches, and the species can shift its coloration somewhat depending on temperature, a process called metachrosis. In the nominate subspecies the belly is white, and the base of the rattle is brown in adults.

Within the United States, the sidewinder is found in the desert of southeastern California, southern Nevada, southwestern Utah, and western Arizona; in Mexico it occurs in western Sonora and eastern Baja California. The snake also inspired the name of the AIM-9 Sidewinder missile, as both use infrared sensing to track a target.

Behavior and diet

The sidewinder's name comes from its distinctive form of locomotion, thought to improve traction on loose desert sand, though the snake actually uses this sideways movement on any surface it can cross quickly. As it moves, its body leaves a series of J-shaped tracks in the sand, with the hook of each J pointing the direction of travel. This same sidewinding gait shows up in other sand-dwelling desert snakes, such as the horned adder and Peringuey's adder, and many other snake species can adopt it temporarily on slick surfaces like mud. On sandy inclines, the sidewinder can increase how much of its body touches the ground to compensate for looser sand, letting it climb steep slopes without slipping.

Sidewinders are nocturnal during the hottest months and switch to daytime activity in cooler months, roughly November through March, and this active period likely runs longer in the southern part of their range. Juveniles hunt using a behavior called caudal luring, wiggling their tails to mimic a moth's flutter or a caterpillar's slower movement and draw in lizard prey; adults abandon this trick once they shift to a diet dominated by desert rodents, birds, and other snakes. Newborn sidewinders show a striking group behavior not seen in other snake species: for about their first week of life, litters mass together at the entrance of their natal burrow, and their collective movement maintains a stable average temperature around 32 degrees Celsius, letting them occupy a spot that would otherwise be lethally hot for a single snake.

Females can produce up to 18 young in a litter, averaging around 10, born live and wrapped in thin membranes they quickly shed. Mating occurs mainly in April and May and sometimes in fall; both sexes reach maturity at two to three years old, and females capable of reproducing annually sometimes skip a year or two if food is scarce. Young are born in late summer to early fall, measuring 6 to 8 inches, and stay near the natal burrow for 7 to 10 days until their first shed, after which they disperse and have no further contact with their mother or littermates. Sidewinders rarely encounter one another outside the mating season despite living at densities of up to one snake per hectare. In the wild, females typically live only around 5 years, often dying of exhaustion after giving birth, while males can live up to 13 years; in captivity, with steady food, sidewinders of either sex can live more than 20 years.

The sidewinder is venomous, though its venom is weaker and its venom glands smaller than in many larger rattlesnake relatives, making it comparatively less dangerous — though any rattlesnake bite can still be serious and calls for prompt medical attention. Reported venom yields average around 30 to 33 milligrams per bite, with a maximum of up to about 80 milligrams. A bite can cause pain, swelling, blood blister formation, and bruising, and in some cases nausea, dizziness, chills, blood-clotting problems, or shock; an antivenom developed for North American pit vipers has been widely available since 2001.

Range and habitat

In the United States, the sidewinder inhabits the desert region of southeastern California, southern Nevada, southwestern Utah, and western Arizona. Across the border in Mexico, it is found in western Sonora and eastern Baja California. It is closely tied to desert habitat, often found in areas of loose, drifting sand where its sidewinding movement and horn-shaded eyes serve it well.

Conservation status

The sidewinder is classified as Least Concern on the IUCN Red List, based on its wide distribution and presumed large population; when last assessed in 2007, its population trend was considered stable. The species is not listed as facing significant decline.