Mojave Rattlesnake

Crotalus scutulatus grows to an average total length (tail included) of less than 100 cm (3.3 ft), with a maximum total length of 123.6 cm (4.1 ft) for males and 92.2 cm (3.0 ft) for females.

There is no single visual trait that reliably identifies C. scutulatus and the most reliable visual identifications result from careful consideration of multiple traits. C. scutulatus is broadly sympatric with C. atrox (the Western Diamond-backed Rattlesnake), which it closely resembles. The dorsal color of C. scutulatus varies from shades of green to browns, grays, and even yellowish. C. scutulatus has a row of large diamond-shaped dorsal blotches closely resembling C. atrox but lacking the abundant dark speckling, both coarse and fine, found throughout the dorsal surfaces of C. atrox. Additionally, C. scutulatus lacks the white margins along the caudal edges of the dorsal "diamonds" that are found in most C. atrox. The postocular light facial stripe usually bends toward the neck and does not intersect with the mouth in C. scutulatus, as it does in C. atrox. The tail is usually marked with alternating pale and dark rings in both species, with the dark rings often (but not always) being narrower than the pale ones in C. scutulatus and the colors are usually less distinct than the bright white and dark black caudal rings of most C. atrox. …

Crotalus scutulatus is found in arid habitats in the southwestern United States, from the Mohave Desert in California's Los Angeles and San Bernardino Counties, across most of western and southern Arizona (southwest of the Mogollon Rim), and from El Paso County south through the Big Bend region of western Texas. It also occurs as far north as Lincoln County in Nevada, the southwest corner of Washington County in Utah, and portions of extreme southern New Mexico. In Mexico, it is found in Sonora, Chihuahua, and south on the Mexican Plateau to the states of Mexico, Puebla, and Veracruz. It is found in deserts and other areas with xeric vegetation from near sea level to about 2,500 m (8,200 ft) elevation.

Crotalus scutulatus is most active from April to September. They are ambush predators, eating mostly small rodents and lizards. Courtship begins in late summer/fall, is interrupted by winter, and resumes in the spring. Females bear live young, from two to 17 (average about eight), from July through September. This species is not known to den communally and they have no need to seasonally migrate between winter dens and summer foraging areas, as do some other species living at higher elevations and higher latitudes. Instead, individuals occupy well defined home ranges year around, taking shelter during the winter and hot summer weather in burrows excavated by animals like rodents, tortoises, and kit foxes. Like other rattlesnakes, this species is routinely preyed upon by larger predators like coyotes, bobcats, and raptors. As a result, it is shy, cryptic, and does not seek out confrontations with larger creatures, including humans. But like other rattlesnake species, it will strike and bite vigorously when disturbed, especially if surprised or when there is no nearby vegetation or burrow into which the snake can escape.

For decades, the bite of Crotalus scutulatus has been considered to be extraordinarily deadly, often described as "the" (or "one of the") deadliest or most dangerous rattlesnakes. For example: "the most lethal of the North American rattlesnake venoms"; "one of the most lethal venoms among the world's reptiles"; "an extremely dangerous snake"; "probably the most dangerous snake in the United States"; and "considered among the most venomous snakes on Earth". Such claims are usually attributed to the neurotoxin produced by most populations of C. scutulatus in the United States and Mexico, which has been reported to be capable of causing delayed respiratory paralysis with little or no local tissue injury. This neurotoxin was isolated and described in 1975 and named "Mojave toxin". In 1978, an area in southcentral Arizona was identified where the venom of C. scutulatus is significantly less lethal to laboratory mice than venom from the balance of the species' range. The more lethal (and more widely distributed) variant was named "venom A" and the less lethal variant was named "venom B". The difference in lethality was later determined to be lack of Mojave toxin in the venom B population. Thus, venom A became known as the neurotoxic variant and venom B became the non-neurotoxic variant. In addition to the absence of Mojave toxin, C. …