Western Diamond-backed Rattlesnake

Western Diamond-backed Rattlesnake, Crotalus atrox

Western Diamond-backed Rattlesnake, Crotalus atrox. Snake photographed within the confines of the Arizona-Sonora Desert Museum, Tucson, Arizona, February, 2022.

The Western Diamond-backed Rattlesnake, Crotalus atrox, is a member of the Viperidae family of Pit Vipers. The Viperidae family consists of three-hundred and forty-three members placed in four subfamilies and thirty-five genera. Members of the Viperidae family are venomous and are commonly known as vipers. They are characterized by a head that is distinct from the body and a single pair of long, hollow, venom-injecting fangs that can be folded against the top of the mouth (tipped inward) when their mouth is closed. There are forty-four species in the Crotalus genus. The Western Diamond-backed Rattlesnake is known in Mexico as Víbora-cascabel de Diamantes.

Western Diamond-backed Rattlesnakes are large and heavily bodied. They have three to eight small scales between their supraocular scales, keeled dorsal scales, and an undivided anal plate. Their head is broad, arrow-shaped and distinct from their neck. Heat sensing pit organs lie between their eyes and their nostrils. Their base color often blends with their environment, from dull gray, to tan, to reddish. Two diagonal light stripes extend from each eye to their jaw. Their dorsal scales are peppered with dark spots and marked with dark, pale-bordered, diamond-shaped patterning with a light center. Their tail has black and white banding of nearly equal width with a terminal rattle. Some individuals living near deserts may become so pale that their markings are obscured except for the white borders of the diamond pattern. Sexual dimorphism is displayed with males and females maturing at a snout to vent length of 51.2 cm (20 inches) and 54.1 cm (21 inches), respectively. Additionally, males grow to a larger size and have three to eight black tail bands (females have two to six). Adults can grow to more than 2.0 m (6 feet 6 inches) long, but most average between 1.2 m (3 feet 11 inches) and 1.8 m (5 feet 11 inches).

Western Diamond-backed Rattlesnakes are more diurnal in the spring and fall, with greater nocturnal or crepuscular activity in the summer. They hibernate through the winter primarily in abandoned burrows of other animals, which they turn into communal dens. Sometimes they can be found in burrows occupied by mammals, such as Gophers and Prairie Dogs. Mating takes place before and after denning in March through May and August through September. Males engage in ritual combat for access to females. Copulation may take hours to complete, and fertilized eggs are retained within the female’s body. Hatching occurs within the female, before the young are born alive. Litters average between two to twenty-five young during June into early October. Females commonly reproduce every other year, but they may give birth yearly in times when food resources are plentiful. Young are precocial and are left to fend for themselves after only a few hours. Juveniles measure between 20.3 cm (8.0 inches) and 36.7 cm (14 inches) in length and resemble small adults, but may be more brightly patterned. Although some individuals can live for more than 22 years in captivity, they have life spans of 20 years in the wild.

Western Diamond-backed Rattlesnakes locate their prey by olfaction and infrared receptors (pit organs) located between their eyes and nostrils. Their pit organs detect warm-blooded creatures in their immediate environment. They prey upon a variety of animals including rabbits, rodents, ground birds, other reptiles, invertebrates, amphibians, and fish. In turn, they are preyed upon by birds of prey (such as Eagles and Hawks), Foxes, and Bobcats. Additionally, they are trampled to death by larger mammals, such as Deer and Horses, who are threatened by their presence. If disturbed, they may coil, rattle their tail, and raise the anterior portion of their body in a defensive posture ready to strike any adversary. They are often quick to bite if threatened.

The Western Diamond-backed Rattle-snake is one of the most commonly observed snakes throughout its range. They occur in the United States from southeastern California, central Arizona, New Mexico, Texas, Oklahoma, and Arkansas. In Mexico, they occupy extreme northeastern Baja California, northern Sinaloa, Veracruz, and Oaxaca. Their elevational range extends from sea level to 2,440 m (8,000 feet). They inhabit arid and semi-arid regions including desert, grassland, shrubland, woodland, open pine forest, river bottoms and coastal islands. They are commonly found near rocks on bajadas, low hills, and arroyos.

The Western Diamond-backed Rattlesnake may be confused with the Mojave Rattlesnake, Crotalus scutulatus, due to their similar appearances and overlapping ranges. These species can be differentiated visually. The Mojave Rattlesnake also has a banded tail, however, their light bands are broader than their dark bands. They have a light stripe behind their eyes that ends posterior to the corner of their mouth, and their dorsal scales are not speckled. Additionally, they have two (rarely three) large scales behind their supraoculars anteriorly.

From a conservation perspective, the Western Diamond-backed Rattlesnake is considered to be of Least Concern due to their wide distribution and presumed large population size. No major threats have been identified for this species. Some local populations have been decimated by habitat destruction, automobile traffic, and direct killing by humans, especially in conjunction with “rattlesnake roundups”. Caution: Western Diamond-backed Rattlesnakes are known for their aggressive nature and their willingness to bite those who threaten them. Their venom is highly hemorrhagic and human bites can be fatal, even with medical treatment. Their venom can cause pain, swelling, and necrosis at the site of the bite, as well as renal damage and problems with blood coagulation. Western Diamond-backed Rattlesnakes bite hundreds of people throughout the southwestern United States and northern Mexico every year, and approximately 10 to 20% of untreated bites are fatal. If encountered, extreme caution must be used.