Crotalus oreganus helleri - Southern Pacific Rattlesnake

Venomous

The venom of this snake is potentially dangerous to humans.

Size

Adults 30 - 44 inches long, sometimes up to 54 inches. Newborns about 10 inches long.

Appearance

A heavy-bodied, venomous pit viper, with a thin neck and a large triangular head. Pupils are elliptical. Scales are keeled.

Ground color is brown to olive-brown. Dark brown blotches, completely outlined by light pigment, mark the back. These blotches turn to bars toward the tail, which is surrounded with dark rings. The last ring is not well-defined and is more than twice the width of the other rings. Young have a bright yellow tail. The underside is pale, sometimes weakly mottled.

A rattle, consisting of loose interlocking segments, usually occurs at the end of the tail. A new rattle segment is added each time the skin is shed. Newborn snakes do not have a rattle - just a single button which does not make a sound.

Heat sensing pits on the sides of the head help the snake to locate prey by their warmth. Long, hollow, movable fangs connected to venom glands inject a very toxic venom which quickly immobilize prey. The snake can control the amount of venom injected and the fangs are replaced if broken. Bites on humans are potentially dangerous without immediate medical treatment. Even a dead snake can bite and inject venom if the jaws reflexively open when they are touched.

Behavior

Primarily nocturnal and crepuscular during periods of excessive daytime heat, but also active during daylight when the temperature is more moderate. Not active during cooler periods in Winter.

Prey is found while the snake is actively moving, or by ambush, where the snake waits near lizard or rodent trails, striking at and releasing passing prey. The snake then follows the trail of the envenomated animal and swallows it whole.

When alarmed, a rattlesnake shakes its tail back and forth. The movement rubs the rattle segments together producing a buzzing sound which serves as a warning. Juveniles are born with only a silent button at the end of the tail.

Diet

Eats birds, lizards, snakes, frogs, insects, and small mammals, including mice, rats, rabbits, hares, and ground squirrels. (Adult California Ground Squirrels are immune to rattlesnake venom and will intensely confront any snake they feel to be a threat.)

Reproduction

Live-bearing; young born August - October. Known to hybridize with the Northern Mohave Rattlesnake where their ranges overlap in the Antelope Valley.

Range

This subspecies, Crotalus oreganus helleri - Southern Pacific Rattlesnake, is found in California from Santa Barbara County, where there is a wide zone of intergradation with the Northern Pacific Rattlesnake north to around Morro Bay, east to the central valley and the desert slopes of the transverse and peninsular ranges, and south into the middle of the Baja California peninsula. Ranges north of the transverse ranges into the Mojave Desert in the Antelope Valley and just south of Barstow. Also found on Santa Cruz and Santa Catalina Islands, both of which are popular vacation destinations.

The species Crotalus oreganus - Western Rattlesnake, occurs from the Pacific Coast of northern Baja California north through most of California except the southern deserts, through Oregon and eastern Washington into British Columbia, Canada, and east into Nevada, Idaho, Utah, northern Arizona, extreme southwestern Wyoming, and extreme northwestern New Mexico.

Habitat

Found in a wide range of habitats from seaside dunes, to desert scrub, grassy plains, rocky hillsides, chaparral, open woodlands, and agricultural areas.

Taxonomic Notes

The taxonomy of Western Rattlesnakes is controversial and still being studied.

Some researchers still use the species Crotalus viridis and this snake remains Crotalus viridis helleri .