Aquarium of the Pacific - Online Learning Center - Species Print Sheet
Conservation Status: Safe for Now
Southern Pacific Rattlesnake
(Crotalus oreganus helleri)Reptiles
The Southern Pacific rattlesnake, one of the largest rattlesnakes, is one of several dangerously venomous rattlesnakes species native to California. Their venom is highly toxic to humans and occasionally fatal; however, they strike humans only if cornered or threatened.
At the Aquarium
Not on exhibit. Information about this rattlesnake is included in the Online Ocean Learning Center for use as a reference.
Southern Santa Barbara County to northwestern Baja California, Mexico. Also Santa Cruz and Santa Catalina Islands.
These rattlesnakes live in a variety of areas including grasslands, mountain forests, coastal dunes, rocky deserts and hillsides, and agricultural fields. In the northern end of their range they spend the winter hibernating in rock crevices and ledges. Many individuals (sometimes hundreds) will gather together in “snake dens” to over-winter.
The thick body of Southern Pacific rattlesnakes ends in a short stubby tail. The rattles at the end of the tail are made up of a series of loosely jointed, dry, hollow segments of skin. Narrow ridged (keeled) scales cover the entire body. The large triangular head widens at the base. Fangs are contained in the front of the mouth. The neck is thin. Heat sensing pits are located on each side of the head. The pupils of the eyes are elliptical. The tail of young juveniles ends in a soft prebutton (an extra large scale) instead of a rattle. When the snakes shed their skin for the first time at one to two weeks after birth, another scale, the button, emerges. The button is the first segment of a rattlesnake’s rattle.
Most of these rattlesnakes blend into their surroundings due to their coloration. Although usually brown to olive-brown, they may be gray or a greenish tint. A thin brown, grey, or black stripe extends from the corner of each eye to the mouth.covers their eyes. Large, dark-rimmed spots of brown, olive, tan, grey, or black cover the back. The spots narrow into strips toward the tail. Very young snakes in this species usually have a bright yellow-green tail. Southern Pacific rattlesnakes found on Santa Catalina Island are usually almost completely black, lacking patterns.
Adults are usually 75 to 100 cm (30 to 44 in) long. Some individuals grow to be over 135 cm (54 in) in length.
Rattlesnakes eat only when they are hungry. If their last meal was large, adults can go two weeks between meals. Juveniles usually eat once a week. Young snakes feed mostly on small lizards, while adults usually eat small mammals, birds, and other snakes. Rattlesnakes usually are nocturnal hunters. One way that they track passing prey in the dark is by flicking their forked tongue in and out to pick up of ground odors that come from the potential meal. The smell is transmitted to organs in the roof of the mouth that connect to the brain. These snakes also catch a meal by hiding near their prey’s territory and ambushing it. Usually, one bite is enough to kill the victim before it can run or fly away.
See the Adaptation section for another way that rattlesnakes find and track prey.
Rattlesnakes have complex breeding behaviors. In the spring a female ready to mate releases chemicals called pheromones.. Male rattlesnakes smell the pheromones and pursue the female. If two males compete for the same female, they may perform a combat dance. In this display the two males coil around each other and push up to a third of their bodies over the ground. Since the snakes have no limbs to maintain their balance, both snakes promptly topple over. This encounter can be repeated for over 30 minutes. Eventually, one snake, usually the smaller of the two, retreats. The other snake continues to look for the female. Once he finds her, he courts her by touching her with his tongue and rubbing her back with his chin.
Fertilization is internal. Unlike many snakes, most rattlesnakes are ovoviviparous. About 90 days after mating, 9-10 live, well-developed young (7 to 10 in) long are born. They are dangerous from birth as a result of being born with short fangs and the ability to inject venom. They usually stay in the area where they were born for about two weeks which is when their first molt commonly occurs and they begin forming their rattle.
Since they are cold-blooded, rattlesnakes are only as warm or as cold as their environment. To maintain an ideal body temperature, rattlesnakes move into sunlight or shade throughout the day. By hunting and moving mostly at night, they avoid very warm daytime temperatures. Night hunting when the ambient temperature is cooler also allows their heat sensitivity to be at peak performance.
All rattlesnakes are pit vipers. They have a heat receptive pit or organ between each eye and nostril covered by a thin membrane that is sensitive to infrared radiation. This sixth sense “tells” these cold-blooded snakes when their body temperature is above or below the surrounding environment. The snakes seek sunlight or shade depending on what the organs sense. Their sixth sense also enables them to “see” the heat signature of a potential prey animal or the heat trail it left behind on the ground as it ran away after being bitten by the snake. Rattlers can track their dying victim over fairly rugged terrain and comparatively long distances.
The rattle at the end of the tail of southern Pacific rattlesnakes is made up of segments of keratin. When the snakes shed their skin, a new segment of the rattle is formed. The rattle warns other animals the snake is venomous and can and will defend itself. It is thought that the rattle may also prevent trampling of the snake. For example, American bison are very in tune with the particular sound of a snake rattle and will avoid it.
Rattlesnake venom is another important adaptation. The two long, hollow, hinged fangs at the front of the mouth are normally folded into a groove in the roof of the snake’s mouth. When a rattlesnake strikes, the fangs unfold snapping forward at a 45o angle. Once the fangs make contact, glands attached to the venom duct (a pathway from the venom glands to the fangs) contract, injecting the toxin. These snakes are able to control the amount of venom injected, usually injecting 20-25% of their supply at a time.
Disease, predation, and accidents kill many rattlesnakes. As a result, many snakes only live for a few years. In protected environments, however, rattlesnakes can live between 10 and 20 years.
Southern Pacific rattlesnakes are not listed as threatened or endangered either by the IUCN Red List or California Fish and Game. Unfortunately, due to increasing road construction and human ignorance, rattlesnakes are on the decline in almost every environment where they are found. Without these stealthy predators as a natural control, it the rodent population may increase threatening human food supplies and other wild flora and fauna.
Other than humans, rattlesnakes are commonly preyed on by birds of prey, coyotes, and Roadrunners, (Geococcyx californianus.
Much of our current-day technological advances in night-vision and heat seeking ability are a result, in part of research done on pit vipers such as the southern Pacific rattlesnake.
Southern Pacific rattlesnakes’ venom changes as they age. While the snakes are young, their venom is less potent and does not digest prey very quickly. As the snakes age and favor faster, harder to digest prey, the venom becomes stronger, adapting to the need to hunt larger and different prey to satisfy their appetites.