Western Rattlesnake

Crotalus oreganus, commonly known as the Western rattlesnake or northern Pacific rattlesnake, is a venomous pit viper species found in western North America from the Baja California Peninsula to the southern interior of British Columbia.

Scientific Classification

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Squamata

Suborder: Serpentes

Family: Viperidae

Subfamily: Crotalinae

Genus: Crotalus

Species: Crotalus oreganus

Description

The size of this species varies greatly, with some populations being stunted and others growing very large. Mainland specimens often reach 100 cm (39 in) in length, with the largest on record being 162.6 cm (64.0 in) (Klauber, 1956) for C. o. oreganus. The species also varies in size in relation to its migration routes as individuals with longer and more linear paths tend to have more mass. The C. oreganus is classified with 6 subspecies with 3 of them being present within the state of California.

This species, in its various forms, shows considerable ontogenetic variation. Juveniles usually have more or less distinct patterns, but these fade as the animals mature. The color of the iris often matches the ground color, which may be bronze, gold, or different shades of tan, pink, or gray.

The habitat and/or the substrate of the Crotalus oreganus determines their coloration. The color pattern of the typical form, C. o. oreganus, has a dark-brown, dark-gray, olive-brown, or sometimes black or pale yellowish ground color overlaid dorsally with a series of large, dark blotches with uneven white edges. These blotches are also wider than the spaces that separate them. Additionally, a lateral series of blotches, usually darker than the dorsal blotches, is clearly visible on all but the darkest specimens. The first rings of the tail are about the same color as the last body blotches, but these rings become progressively darker; the last two rings, at the base of the tail, are usually black. The belly is pale yellow, usually with brown spots. A large, dark-brown blotch on the snout has a pale border behind it that forms transverse bars on the supraoculars. There is a dark brown postocular stripe with a white border that extends from the eye to around the angle of the jaw.

Common names

Efforts to standardize the common names of North American reptiles and amphibians began as early as 1956, and the name "Northern Pacific Rattlesnake" was applied to Crotalus viridis oreganus with wide acceptance. Following subsequent taxonomic changes, and depending on various taxonomic arrangements, the names "Northern Pacific Rattlesnake" or "Western Rattlesnake" have been applied with high levels of consistency and acceptance (largely depending on which arrangement, and recognition of subspecies if any, in the Crotalus viridis complex are followed), although occasionally appearing in slight variations, e.g. north Pacific rattlesnake. In addition, C. oreganus can be referred to as “California rattlesnake, Great Basin rattlesnake, Missouri rattlesnake, Oregon rattlesnake, black rattlesnake, black diamond rattlesnake, black snake, confluent rattlesnake, Hallowell’s rattlesnake, southern rattlesnake, western black rattlesnake, and western rattler.

Geographic range