Sidewinder

In sidewinding, the snake anchors two short sections of its body against the ground while lifting and swinging the rest forward and to the side, then sets those loops down at an angle and lifts the previously anchored parts, so the whole body flows diagonally across the surface like a rolling spring. Because only two small parts of the snake touch the ground at any instant, and those parts are set down and lifted without sliding, the gait grips loose sand that a normally crawling snake would just push around, and it keeps most of the body off ground hot enough to injure the animal. It is also fast and cheap in energy terms. Sidewinding is mainly used by snakes that live on wind-blown sand, and it has evolved independently in the American sidewinder, the African and Middle Eastern horned vipers, and others.

It has hornlike scales, not true horns. Above each eye is a single enlarged, pointed, upward-curling scale (the supraocular), which gives the snake its other common name, the horned rattlesnake, and a slightly devilish look. The scales are movable and can be folded flat down over the eye. Their exact function is not fully settled, but the leading ideas are that they shade the eye from the intense desert sun, protect the eye from abrasion by sand when the snake shuffles down into the sand to bury itself, and keep sand out of the eye as the snake moves through rodent burrows. Not all individuals have equally developed "horns," and a few other vipers around the world have convergently evolved similar structures.

Sidewinders are venomous rattlesnakes, and a bite requires medical treatment, but they are among the less dangerous rattlesnakes to people. They are small, which limits how much venom they can deliver, and their venom is generally less potent by volume than that of larger species like the Mojave or western diamondback rattlesnakes. A bite typically causes significant local pain, swelling, and tissue effects and can cause systemic symptoms, and antivenom may be needed, but fatalities are very rare. Sidewinders are also not aggressive; they rely on camouflage and stillness, will rattle and retreat if they can, and most bites happen when the snake is stepped on or deliberately handled. Watching where you put your hands and feet in sandy desert, especially at dusk and at night when sidewinders are active, is the main precaution.

In the sandy deserts of the American Southwest — the Mojave, Sonoran, and Colorado deserts of California, Nevada, Utah, and Arizona, and into northwestern Mexico — specifically on and around loose sand — dunes, sandy flats, hummocks around desert shrubs, and the sandy bottoms of washes. They avoid hard, rocky ground. Sidewinders are largely nocturnal in the hot months and shift to being active in the daytime in spring and autumn. During the day in summer they rest in the shade of a bush or, very commonly, coiled in a shallow self-dug pit at the base of a shrub or in the open, with only the top of the head and the eyes exposed, waiting to ambush a rodent. The distinctive J-shaped tracks in the morning sand are often the only sign that one passed through.