This rattlesnake is in a defensive position, head back, ready to strike,
rattling its tail, and puffing itself up to look bigger and more threatening.
Click on the second photo to see an example of it expanding its size.
This adult was crossing an unpaved road one morning at the eastern edge of San Diego County. When I startled it,
it made a quick U-turn and crawled into a bush, leaving me a good look at the tracks it made in the sand.
Adult, San Diego County
Juvenile with yellow tail, Los Angeles County
(Note that the rattle consists of only one segment which does not produce a sound.)
There are stories circulating that rattlesnakes are evolving and losing their rattles because they no longer use them due to the fact that it's safer for them to remain silent around humans. There's no real proof that this is happening. Here's more information about that.
The tail of a newborn juvenile has only a single silent yellow button on the end of its tail. As it grows it will add rattle segments at the end of the tail behind the button, which remains at the end.
Juvenile tail and snall rattle
Unusual or Interesting Color and Pattern Variations
Click on the picture to see more
Rattlesnakes are important members of the natural community. They will not attack, but if disturbed or cornered, they will defend themselves. Reasonable watchfulness should be sufficient to avoid snakebite. Give them distance and respect.
"Rattlesnakes are also among the most reasonable forms of dangerous wildlife: their first line of defense is to remain motionless; if you surprise them or cut off their retreat, they offer an audio warning; if you get too close, they head for cover. Venom is intended for prey so they're reluctant to bite, and 25 to 50 percent of all bites are dry - no venom is injected."Leslie Anthony. Snakebit: Confessions of a Herpetologist. Greystone Books, 2008.
Rattlesnakes are typically described as poisonous, but they are actually venomous.
A poisonous snake is one that is harmful to eat. A venomous snake injects dangerous venom into its victim.
A bite from a rattlesnake can be extremely dangerous, but rattlesnakes should not be characterized as aggressive and vicious, striking and biting without provocation, as they are often shown. If rattlesnakes are given some space and enough time to escape to a safe place, they will usually just crawl away as fast as possible to avoid confrontation. Rattlesnakes will not strike without a reason: they will strike at a potential meal and they will defend themselves from anything they perceive as dangerous. They avoid striking and biting because it uses up their valuable supply of venom which they need to kill and digest their food.
Rattlesnakes are often portrayed with the body partly coiled, the tail rattling loudly, and the head raised up and ready to strike, but they do not need to coil up this way to strike and bite. This display is a warning not to come any closer. It's a defensive behavior that some rattlesnakes use when they sense that crawling away would put them in danger of attack.
Rattlesnakes do not always rattle a warning. Sometimes they rattle loudly to warn potential enemies of their presence, but other times they remain silent when they sense a threat, choosing to remain still to rely on their cryptic color and pattern to let them blend into their surroundings to hide from the threat. Making a noise in this situation risks advertising their presence. They also use their natural camouflage to hunt by sitting still, without rattling, trying to remain invisible as they wait for a warm-blooded prey animal to pass close enough to strike.
Dangerously Venomous(Commonly but inaccurately called "Poisonous.")
A bite from this snake can be very dangerous without immediate medical treatment. Treatment can require hospitalization and great expense.
Adults 30 - 44 inches long, sometimes up to 54 inches. Neonates are about 10.5 inches in length (27 cm) (Bartlett, 2009).
A heavy-bodied pit viper, with a thin neck, a large triangular head, and a rattle on the end of the tail consisting of loose interlocking hollow segments.
A new rattle segment is added each time the skin is shed, which can be more than one time per year.
Pupils are elliptical.
Scales are keeled.
Rattlesnakes are "pit vipers" which means they have two pits that are used to sense heat when hunting warm-blooded prey - with one pit on each side of the front of the head above the mouth.
Color and Pattern
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 tail ring is not well-defined and is more than twice the width of the other rings.
The underside is pale, sometimes weakly mottled.
Young are born with a bright yellow tail with no rattle - just a single button which does not make a sound. They grow rattles and lose the yellow color as they age.
The pattern is brighter on juveniles than on adults.
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.
Radiotelemetry studies have shown that the home range of male snakes is larger than that of females.
Fangs and Venom
Rattlesnakes have long, hollow, movable fangs connected to venom glands. The fangs are replaced if broken. A snakes uses its fangs to inject a toxic venom which quickly immobilize its prey. A rattlesnake can control the amount of venom injected.
Bites that inject venom into humans are potentially dangerous without immediate medical treatment.
Sometimes a rattlesnake bites but does not inject venom. These are called "dry bites." A dry bite may still require medical attention.
Even a dead snake can bite and inject venom if the jaws open and close reflexively when they are touched.
A bite from any kind of rattlesnake of any age or any size should be treated as a serious medical emergency, but the bite of a juvenile rattlesnake is not more dangerous than the bite of an adult.
Experts disagree whether or not juvenile rattlesnake venom is more potent than adult rattlesnake venom, but this does not really make much difference in the severity of a bite.
While adult rattlesnakes can control the amount of venom they inject depending on their needs (small animals need less venom, a defensive or warning bite may need no venom, etc.), it is often assumed that juvenile rattlesnakes do not have the same ability and that they always inject the full amount of venom they have available. Some studies show this is not true.
There is also no proof that adult rattlesnakes are more likely than juveniles to bite without injecting venom when they are biting as a warning. Regardless of these things, adults have far more venom to inject than juveniles so the potential danger from the bite of an adult is significantly higher than the danger from the bite of a juvenile. Even when an adult does not inject the full amount of venom it has available, it most likely injects more venom than a juvenile would inject.
Apparently not all Southern Pacific Rattlesakes have the same type of venom, and this has been found in other species, also. National Geographic 1/27/14
Sunagar, Undheim, Scheib, Gren, Cochran, Person, Koludarov, Kelln, Hayes, King, Antunes & Fry. 2014. Intraspecific venom variation in the medically significant Southern Pacific Rattlesnake (Crotalus oreganus helleri): Biodiscovery, clinical and evolutionary implications. Journal of Proteomics. 2014.
Sound - The Rattle
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.
A new rattle segment is added each time the skin is shed, which can be more than one time per year.
Diet and Feeding
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.)
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.
Pits on the sides of the head sense heat. These heat sensors help the snake to locate warm-blooded prey by their temperature.
Rattlesnakes are ovoviparous or live-bearing. The mother keeps her fertilized eggs inside her body and gives birth to living young.
Mating typically occurs in the spring. Males search extensively for females during the mating season.
Females probably start bearing young at three years of age and breed annually. (Klauber, 1982)
An average litter consists of 4 to 12 young which are born from August to October. (Stebbins & McGinnis, 2013)
Neonates are about 10.5 inches in length (27 cm) (Bartlett, 2009).
Male "Combat Dance"
Adult males engage in a ritual "Combat Dance" during the spring breeding season and at other times. Throughout much of history this activity was presumed to be a mating male and female instead of two competing males. Despite the common name, it is not combat as neither male is injured. And it's not a dance, it's essentially a wrestling match in which necks and forebodies are intertwined, with the stronger snake slamming the smaller one to the ground until the weaker snake leaves the area. Most bouts end in a draw.
"Certainly the presence of a female is not necessary to stimulate males to dance."
"Dancing is not restricted to a single season of the year."
Found in a wide range of habitats from seaside dunes, to desert scrub, grassy plains, rocky hillsides, chaparral, open woodlands, and agricultural areas.
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.
Known to hybridize with the Northern Mohave Rattlesnake where their ranges overlap in western Antelope Valley. (Stebbins, 2003)
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 Idaho, Nevada, Utah, southwestern Wyoming, western Colorado,and northern Arizona.
Crotalus viridis [oreganus] has been found from sea level to around 11,000 ft. (3,350 m.) (Stebbins, 2003)
In 2010, a new elevation record for C. oreganus (lutosus) was documented at 12,112 ft. (3962 m.) Wheeler Peak, Great Basin National Park, White Pine County, Nevada. (Herpetological Review 41(1), 2010)
Notes on Taxonomy
The taxonomy of Western Rattlesnakes is controversial with several different theories. Some of these theories recommend making the three subspecies found in California full species, but this has not been widely accepted. Instead, most authorities seem to favor the split of the Western Rattlesnake species Crotalus viridis into two species - Crotalus viridis, and Crotalus oreganus.
Some authorities still use the former species name Crotalus viridis, recognizing the subspecies covered on this page as Crotalus viridis helleri.
A study published in February 2016* used head shapes and genetic analyses to determine that there are 6 full species of western rattlesnakes found in the former Crotalus viridis complex and suggested the following names, with the three species found in California shown here at the top of the list.
If this taxonomy is accepted, the ranges and common names of western rattlesnakes found in California will remain the same, but they will be full species instead of subspecies.
* Mark A. Davis, Marlis R. Douglas, Michael L. Collyer, Michael E. Douglas. Correction: Deconstructing a Species-Complex: Geometric Morphometric and Molecular Analyses Define Species in the Western Rattlesnake (Crotalus viridis). PLOS ONE, 2016; 11 (2): e0149712 DOI: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0149712) A 2002 study** split the Western Rattlesnake species Crotalus viridis into 7 distinct species:
Crotalus oreganus oreganus becomesCrotalus oreganus
Crotalus oreganus helleri becomesCrotalus helleri
Crotalus oreganus lutosus becomesCrotalus lutosus
** Douglas, Douglas, Schuett, Porras, & Holycross
[2002. Phylogeography of the Western Rattlesnake (Crotalus viridis) Complex, With Emphasis on the Colorado Plateau]. Pp. 11-50. In Biology of the Vipers [Schuett, Höggren, Douglas, and Greene (editors). Eagle Mountain Publishing, Eagle Mountain, Utah]
Some naturalists believe that rattlesnakes on Santa Catalina Island are distinct from those on the mainland and will be recognized as a different subspecies once DNA studies are completed. LA Times Article 11/28/09
Alternate and Previous Names (Synonyms)
Timber Rattlesnake (It is not uncommon for a rattlesnake found in a forested area in California
to be called a Timber Rattlesnake. The true Timber Rattlesnake (Crotalus horridus) is not found in California. It occurs from southeast Minnesota down to central Texas and east to northern Florida up to south-central New Hampshire.)
Crotalus - Greek - krotalon - a rattle - refers to the rattle on the tail
oreganus - belonging to the state of Oregon - referring to the type locality, "banks of Oregon or Columbia River" helleri - honors Heller, Edmund
Stebbins, Robert C., and McGinnis, Samuel M. Field Guide to Amphibians and Reptiles of California: Revised Edition (California Natural History Guides) University of California Press, 2012.
Stebbins, Robert C. California Amphibians and Reptiles. The University of California Press, 1972.
Samuel M. McGinnis and Robert C. Stebbins. Peterson Field Guide to Western Reptiles & Amphibians. 4th Edition. Houghton Mifflin Harcourt Publishing Company, 2018.
Stebbins, Robert C. A Field Guide to Western Reptiles and Amphibians. 3rd Edition. Houghton Mifflin Company, 2003.
Behler, John L., and F. Wayne King. The Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf, 1992.
Powell, Robert., Joseph T. Collins, and Errol D. Hooper Jr. A Key to Amphibians and Reptiles of the Continental United States and Canada. The University Press of Kansas, 1998.
Bartlett, R. D. & Patricia P. Bartlett. Guide and Reference to the Snakes of Western North America (North of Mexico) and Hawaii. University Press of Florida, 2009.
Bartlett, R. D. & Alan Tennant. Snakes of North America - Western Region. Gulf Publishing Co., 2000.
Brown, Philip R. A Field Guide to Snakes of California. Gulf Publishing Co., 1997.
Ernst, Carl H., Evelyn M. Ernst, & Robert M. Corker. Snakes of the United States and Canada. Smithsonian Institution Press, 2003.
Wright, Albert Hazen & Anna Allen Wright. Handbook of Snakes of the United States and Canada. Cornell University Press, 1957.
Ernst, Carl. H. Venomous Reptiles of North America. Smithsonian Institution Press, 1999.
Hayes, William K., Kent R. Beaman, Michael D. Cardwell, and Sean P. Bush, editors. The Biology of Rattlesnakes. Loma Linda University Press, 2009.
Hubbs, Brian R., & Brendan O'Connor. A Guide to the Rattlesnakes and other Venomous Serpents of the United States. Tricolor Books, 2011.
Klauber, Laurence M. Rattlesnakes. University of California Press. (Abridged from the 1956 two volume Rattlesnakes:
Their Habits, Life Histories, and Influence on Mankind.) University of California Press, 1982.
Rubio, Manny. Rattlesnake - Portrait of a Predator. Smithsonian Institution Press, 1998.
Walls, Jerry G. Rattlesnakes: Their Natural History and Care. T. F. H. Publications, Inc., 1996.
Eric A. Dugan, Alex Figueroa, and William K. Hayes. Home Range Size, Movements, and Mating Phenology of Sympatric Red Diamond (Crotalus ruber) and Southern Pacific (C. oreganus helleri) Rattlesnakes in Southern California. Pp. 353-364 in W. K. Hayes, K. R. Beaman, M. D. Cardwell, and S. P. Bush (eds.), The Biology of Rattlesnakes. Loma Linda University Press. 2008.
The following conservation status listings for this animal are taken from the November 2020 California "Special Animals List" and the November 2020 "State and Federally Listed Endangered and Threatened Animals of California" list, both of which are produced by multiple agencies and available here: https://www.wildlife.ca.gov/Data/CNDDB/Plants-and-Animals. You can check the link to see if there are more recent lists.
If no status is listed here, the animal is not included on either list. This most likely indicates that there are no serious conservation concerns for the animal. To find out more about an animal's status you can go to the NatureServe and IUCN websites to check their rankings.