Eastern Diamondback Rattlesnake

Lore & Background

The type specimen (holotype) of Crotalus scutulatus is ANSP 7069, in the collection of the Philadelphia Academy of Natural Sciences (formerly one of two specimens of USNM 5027 at the Smithsonian Institution). The type locality is "Fort Buchanan, Arizona." The ruins of Fort Buchanan are in present day Santa Cruz County, Arizona. 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" (the source cuts off). Robust genetic analyses have revealed the population structure of Crotalus scutulatus throughout the species' range, correlating genetic evidence of isolation and subsequent secondary contact of subpopulations with corresponding geologic and climatic events. As a result, four genetically distinct clades among present-day C. scutulatus have been described. The earliest split occurred at the northern margin of the Central Mexican Plateau about 4.1 million years ago (MYA), separating the species into northern and southern subpopulations. Then about 1.8 MYA, the subpopulation now identified as C. scutulatus salvini diverged genetically from the animals on the Central Mexican Plateau. Most recently, the northern subpopulation was divided at the Continental Divide (Cochise Filter) about 1.5 MYA, creating the Mojave-Sonoran clade to the west and the Chihuahuan clade to the southeast.

In Their Own Story

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.

Reader's Guide

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 primarily an inhabitant of broad desert valleys or lower mountain slopes, often found in sparsely vegetated areas containing predominantly creosote (Larrea), sage (Ambrosia), mesquite (Prosopis), various cacti (Cactaceae), and Joshua trees (Yucca brevifolia), as well as juniper (Juniperus) woodland and grassland (Poaceae) habitats in some places. In general, C. scutulatus tends to avoid densely vegetated and extremely rocky areas, preferring relatively flat, open, and xeric habitats.

Did You Know?

• The type specimen (holotype) of Crotalus scutulatus is ANSP 7069, in the collection of the Philadelphia Academy of Natural Sciences, with the type locality being 'Fort Buchanan, Arizona.'
• Crotalus scutulatus is perhaps best known for producing two distinctly different venom types in different populations.
• The earliest genetic split within C. scutulatus occurred about 4.1 million years ago at the northern margin of the Central Mexican Plateau.
• Females bear live young, from two to 17 (average about eight), from July through September.
• The species is not known to den communally and individuals occupy well defined home ranges year around.