Western diamondback rattlesnake

Identification

The western diamondback is a heavy-bodied pit viper with a broad, triangular head, a slender neck and keeled scales¹. It is grey or tan, sometimes with a pinkish, rusty or orange tinge, and has a row of large brown diamond-shaped blotches along the back. The blotches have dark edges, are often outlined in cream and are peppered with dark specks¹. The tail has bold black and white rings of roughly equal width and ends in a rattle, which gains a new segment each time the snake sheds its skin¹.

Most snakes encountered are under about 1.2 m long, and adults are reported to reach 2.29 m². In Arizona the largest recorded was 1.68 m, not counting the rattle¹.

Distribution

This rattlesnake lives in the south-western United States, from south-eastern California, southern Nevada and Arizona east through New Mexico, Texas and Oklahoma to Arkansas³. In Mexico it ranges over much of the north and centre, including Sonora, Chihuahua, Coahuila, Nuevo León and Tamaulipas, with scattered records further south³.

In Arizona it is found from near sea level to about 1,600 m¹. The Reptile Database lists the Tortuga Island rattlesnake of the Gulf of California under this species, although a 2019 genetic study supported treating it as a separate species³.

Habitat

The western diamondback uses many kinds of dry country, including Sonoran, Chihuahuan and Mohave desert scrub, semi-desert grassland and the lower edges of chaparral and evergreen woodland¹. It seems to be most common on bajadas (gravel slopes at the foot of mountains), hillsides and other slopes rather than on the flats¹.

It shelters in rock crevices and rodent burrows, and in winter it hibernates alone or in dens shared with other rattlesnakes^1,4.

Behaviour

It can be active at any time of day or night when conditions suit it. In spring and autumn it is mostly active by day and at dusk, while in hot summer weather it becomes mainly nocturnal¹. It often rests coiled in the partial shade of bushes or cacti¹.

When disturbed it usually stays still to avoid being seen. If that fails, it may raise its head, rattle and slowly back away towards cover¹. Rattlesnakes do not attack people, but they will defend themselves if disturbed or cornered².

Diet

The western diamondback is an ambush hunter that waits coiled beside rodent trails¹. Like all pit vipers, it has a heat-sensing pit on each side of its face, between the eye and the nostril, which detects infrared radiation from warm-blooded prey⁹. In tests with no visual cues, western diamondbacks reacted to a warm, mouse-sized target up to 1 m away¹⁰. It eats mice, rats, ground squirrels, rabbits, lizards and birds, and occasionally amphibians¹. Young snakes sometimes take large insects and frogs².

It usually strikes a rodent, lets it go and then follows its scent trail, which avoids being bitten back. Birds are often held after the strike so they cannot fly away¹.

Reproduction

This species gives birth to live young; the eggs develop and hatch inside the mother^3,4. Females are thought to start breeding at about three years old^2,4. Litters of about 4 to 25 young have been recorded, and newborns have only a silent “button” instead of a working rattle².

Females can store sperm for six years or longer, and in the wild this species sometimes hybridises with the timber rattlesnake³.

Venom and medical significance

The western diamondback is dangerous to people. The Reptile Database notes that it causes most snakebite casualties in North America, and the WHO lists it in Category 1, the highest medical importance, in both the United States and Mexico^3,5. About 70% of its venom is made up of metalloproteinases and serine proteases, which cause bleeding and local tissue damage⁶.

Bites by North American pit vipers can cause pain, swelling and tissue damage, as well as clotting problems, bleeding and shock, and rarely death⁷. Its venom is one of those used to make the main US antivenom⁷. Many bites happen when people handle or harass the snake¹. Anyone bitten must seek medical care immediately.

Conservation

The IUCN Red List classifies the western diamondback as Least Concern, based on an assessment published in 2007⁸. The Animal Diversity Web describes it as a highly successful species that is not currently threatened⁴.

Because people fear rattlesnakes, they have long been killed through bounties, poisons, traps and the destruction of their food and shelter⁴.

Similar species

None of the other snakes on this site live in the Americas. The western diamondback can easily be confused with the Mohave rattlesnake^1,2. In the western diamondback, the light stripe behind the eye slants steeply down to the upper lip, the blotches are “peppered” with dark specks, and the black tail rings are wide¹. In the Mohave rattlesnake, the stripe behind the eye runs back past the corner of the jaw without reaching the lip². The red diamond rattlesnake, where their ranges meet, is usually reddish-brown or red².

Harmless gophersnakes are also often mistaken for rattlesnakes². These differences are not a safe basis for handling any snake.

In captivity

Western diamondbacks are kept in zoos and used as educational animals, and they have lived for more than 20 years in captivity⁴. It is not a suitable pet, and many serious bites happen when people handle rattlesnakes¹.

If you see one, give it plenty of space and let it move away on its own².