Southern Pacific Rattlesnake

Southern Pacific Rattlesnake, Crotalus oreganus helleri

Southern Pacific Rattlesnake, Crotalus oreganus helleri, Juvenile. Length: 30 cm (12 inches), August 2018. Snake caught in a residential backyard in the greater San Diego, California area. This snake was collected mid-day. When placed in the direct sunlight it became very agitated and mobile; when it found shade it curled up and became very tranquil. I did not find this animal to be aggressive toward me. Productive discussion with Gary Nafis, CaliforniaHerps.com indicated that my identification was correct and this this was a nice healthy juvenile with a couple of buttons, indicative that it was born last fall and shed a couple times and has eaten at least a few meals indicative that it knows very well how to strike but elected to utilize the effective “do nothing” strategy hoping that I would go away. It was collected and relocated alive and unharmed to a new location far away from human habitat.

Southern Pacific Rattlesnake, Crotalus oreganus helleri. Length: 50 cm (20 inches), August 20, 2018. Identification reconfirmed by Gary Nafis, Californiaherps.com. Snake caught on camera on a golf course in the greater San Diego area. This snake was highly combative and eventually allowed to go its own way. Photograph courtesy of Rudy McVicker, Valley Center, California.

The Southern Pacific Rattlesnake, Crotalus oreganus helleri, is a member of the Viperidae family of Pit Vipers. The Viperidae family consists of approximately three-hundred and forty-three members placed in four subfamilies and thirty-five genera. Members of the Viperidae family are venomous and are commonly known as vipers. They are characterized by a head that is distinct from the body and a single pair of long, hollow, venom-injecting fangs that can be folded against the top of the mouth (tipped inward) when their mouth is closed. There are forty-four species in the Crotalus> genus. The taxonomy of Western Rattlesnakes is controversial with several different theories, and some older sources may describe the Southern Pacific Rattlesnake simply as Crotalus helleri. The Southern Pacific Rattlesnake is known in Mexico as  Cascabel del Pacifico Sur.

Southern Pacific Rattlesnakes are full-bodied with keeled scales. They have a thin neck and a large flattened, triangular head. They are brown to olive brown in color with dark brown blotches that are completely circled in white dorsally. Towards the tail, these blotches transition into bars surrounded with dark rings. The last ring is not well-defined, and is more than twice the width of the other rings. Their ventral surface is a uniform pale color. The distal end of their tail is equipped with a rattle, which consists of loose interlocking, hollow segments. Their heads have two pit organs, one on each side of their mouth, that are utilized to seek out prey. They have eyes with elliptical pupils and mouths with hollow, movable, and replaceable fangs that are connected to their venom glands. Adults reach 76 cm (2 feet 6 inches) to 1.14 m (3 feet 9 inches) in length, with some individuals growing up to 1.37 cm (4 feet 8 inches) in length.

Southern Pacific Rattlesnakes are primarily nocturnal during warm weather months, and become crepuscular or diurnal during cooler periods of the year. During winter months, they become inactive. Mating occurs in the spring, with males searching extensively for females. Adult males engage in a ritual “Combat Dance” during which their necks and forebodies intertwine. The stronger male slams the smaller male to the ground until the weaker snake leaves the area. Most bouts end in a draw. Females are able to retain fertilized eggs inside of their bodies, and give birth to four to twelve live precocial young from August to October. The young are 25 cm (10 inches) in length and have a bright yellow tail with no rattle. Instead, they have a single button (extra large scale) which does not make a sound. As they mature, they shed their skin once to twice a year, adding a new rattle segment each time. Eventually, they lose their yellow tail color. No additional parental care is provided to the young after birth. While many individuals only live for a few years in the wild, they can live between ten and twenty years in protected environments.

Southern Pacific Rattlesnakes consume birds, lizards, frogs, mice, insects, rabbits, rats, ground squirrels, and other snakes. They locate their warm-blooded prey using the specialized pit organs on their head, which senses heat in their immediate environment. Prey is found while they are actively moving or by ambush, where they wait near lizard or rodent trails to strike and release their prey. They then follow the trail of the envenomated animal and swallow it whole.  The California Ground Squirrel, Otospermophilus beecheyi, is immune to their venom and is known to aggressively confront Southern Pacific Rattlesnakes. They are preyed upon by birds of prey, Coyotes, and Roadrunners.

The Southern Pacific Rattlesnake occurs from Santa Barbara County in southern California, south into the middle of the Baja California Peninsula. Additionally, they are found on Santa Cruz and Santa Catalina Islands. They are known to hybridize with the Northern Mojave Rattlesnake, Crotalus oreganus oreganus, where their ranges overlap in western Antelope Valley, California. Their elevational range extends from sea level to approximately 3,350 m (11,000 feet). They occupy a wide range of habitats including seaside dunes, desert scrub, grassy plains, rocky hillsides, chaparral, open woodlands, and agricultural areas.

In the Northern Coastal Baja, the Southern Pacific Rattlesnake is most likely to be confused with the Red Diamond Rattlesnake, Crotalus ruberm, due to their similar appearances. These species can be differentiated visually. The Red Diamond Rattlesnake lacks light colored circles around their brown blotches and has black and white rings around their tail just before their rattle.

From a conservation perspective, the Southern Pacific Rattlesnake has not been formally evaluated by the IUCN. The Western Rattlesnake, Crotalus oreganus, is currently considered to be of Least Concern due to their wide distribution, tolerance of a broad range of habitats, and presumed large population size. Local populations are threatened by human persecution (especially around urban areas) and habitat loss and degradation from residential, commercial, and agricultural development. Populations in Baja California have been impacted by urbanization, agricultural expansion, and the construction of new roads. CAUTION: The Southern Pacific Rattlesnake is highly venomous and should be considered exceedingly dangerous. A bite requires immediate medical treatment, and may require hospitalization. Note: It is estimated that 7,000 – 8,000 people are bitten each year by venomous snakes in the United States, of which five die.