Top of head showing several small scales between intraoculars. Compare with the two large scales between the supraoculars of the Northern Mohave Rattlesnake.
It has been speculated that C. atrox is present in the deserts of eastern San Diego County and western Imperial County because some snakes in those areas have dark spots in the dorsal diamonds. Some range maps also show C. atrox as present in these areas, and there are a couple of museum records for C. atrox there, so identification based on physical characteristics is difficult if not impossible. (More information about differentiating C. atrox and C. ruber.)
From the coloring and the very dark spots in the dorsal diamonds, this snake appears to be C. atrox, but the first infralabial scales are divided, which is a characteristic of C. ruber. The book says the first infralabial scale is "usually" undivided on C. atrox, which means that sometimes they can be divided. Does that mean that this snake is actually C. atrox? It's probably not possible to know without DNA analysis.
Western Diamond-backed Rattlesnakes From Outside California
Adult in the typical Diamondback threatening
defensive posture, Sierra County, New Mexico.
Adult, Cochise County, Arizona
Adult, Webb County, Texas
Adult, from just across the Colorado River from California in
La Paz County, Arizona
Juvenile eating a rodent on a road at night, Hidalgo County, New Mexico
How to Tell the Difference Between Rattlesnakes and Gophersnakes
Harmless and beneficial gophersnakes are sometimes mistaken for dangerous rattlesnakes. Gophersnakes are often killed unnecessarily because of this confusion.
(It's also not necessary to kill every rattlesnake.)
It is easy to avoid this mistake by learning to tell the difference between the two families of snakes. The informational signs shown above can help to educate you about these differences. (Click to enlarge).
If you can't see enough detail on a snake to be sure it is not a rattlesnake or if you have any doubt that it is harmless, leave it alone.
You should never handle a snake unless you are absolutely sure that it is not dangerous.
California National Wildlife Refuge warning sign, Imperial County.
Click the picture to see more rattlesnake signs.
Short Videos and Sound
Several views of a Cochise County, Arizona Western Diamond-backed Rattlesnake rattling and taking a defensive pose with its head and tail elevated. It keeps rattling as it crawls away into a bush.
A Western Diamond-backed Rattlesnake rattles in a defensive pose in Sierra County, New Mexico.
Listen to an Arizona
Western Diamond-backed Rattlesnake rattle and hiss.
(This is the snake)
California Park warning sign.
Click the picture to see more
rattlesnake signs.
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 touch or 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.
Description
Dangerously Venomous
A bite from this snake can cause death or serious illness or injury in humans that may require immediate medical care.
(Commonly called a "poisonous" snake to indicate that its bite is dangerous, but that is not correct. It should be called a "venomous" snake. A poisonous snake can harm you if you eat it. A venomous snake can harm you if it bites you.)
Size
Adults grow to 30-90 inches (76-229 cm). (Stebbins, 2003)
Most snakes encountered are from 1 to 4 feet in length.
The largest rattlesnake in California, and in the West.
(Only the Eastern Diamond-backed Rattlesnake is larger, growing to 96 inches (243.8 cm) (Stebbins & McGinnis, 2012)
Appearance
A long, 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.
Pupils are elliptical.
Scales are keeled.
Usually 4 or more small scales occur on top of the head between the supraocular scales.
Has two pits, one on each side of the front of the head above the mouth that are used to sense heat when hunting warm-blooded prey.
25-27 scale rows.
Color and Pattern
The ground color and the intensity of the pattern are variable, often matching the habitat; grey, brown, olive, tan, or yellowish.
Diamond-shaped blotches on the back are brown or black, with light edges.
Markings are sometimes indefinite giving a dusty overall appearance.
Broad black and white rings, fairly equal in width, circle a thick tail just before the rattle.
(Commonly called a "coontail" since it resembles the tail of a racoon.)
The ring adjacent to the rattle is usually black.
A light stripe extends from behind the eye diagonally to the upper lip in front of the end of the jaw crossing over the lip.
The light stripe behind the eye on the similar Northern Mohave Rattlesnake extends back beyond the end of the jaw and does not cross the lip.)
Young
The markings on young snakes are more discinct than markings on adults.
Newborn snakes do not have a rattle - just a single button which does not make a sound.
Also similar to and easily confused with the Red Diamond Rattlesnake - Crotalus ruber, but in California the ranges of these two snakes barely meet, and the Red Diamond Rattlesnake is typically light reddish brown or red in color.
Primarily nocturnal during periods of excessive daytime heat, but active during daylight when the temperature is more moderate. Not active during cooler periods in Winter.
Fangs and Venom
Two large hollow movable fangs are located at the front of the upper jaw are folded backwards when not used. The fangs are connected to venom glands so that when the snake bites, the fangs swing forward rapidly to stab the prey and inject a toxic venom that quickly immobilizes the prey. A rattlesnake can control the amount of venom injected. The fangs can be replaced if broken.
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 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.
Venomous snakes are immune to the venom of their own species, so if a snake is bitten during interactions with other snakes of its species during territorial fights or during mating or if it accidentally bites itself, it will not suffer from the venom. However, they are not typically immune to the venom of other species of snakes.
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.
Defense
When disturbed, in self-defense Western Diamond-backs will often aggressively hold their ground, raising the head high in a striking coil with the tail elevated and rattling, and hissing loudly.
Even a dead snake can bite and inject venom if the jaws reflexively open and close when they are touched.
Diet and Feeding
Eats small mammals, birds, and lizards. Juveniles sometimes eat large insects and frogs.
Pits on the sides of the head sense heat. These heat sensors help the snake to locate warm-blooded prey by their temperature.
An ambush hunter, it typically sits near the trail of a mammal, waiting for it to pass by, then strikes at and releases the prey. The snake then follows the trail of the envenomated animal and swallows it whole.
Rattlesnakes are ovoviviparous. The mother keeps her fertilized eggs inside her body and gives birth to living young.
Females probably start bearing young at three years of age and breed annually.
Mating occurs in the spring.
Young are born
between late August and early October. (Klauber, 1982)
Four to 25 young are born in a litter. (Stebbins & McGinnis, 2013)
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."
(Klauber, 1982)
Habitat
In California inhabits only desert areas in the southern Mohave Desert and throughout most of the Sonoran Desert in California. May also be found in areas in the desert modified by urban development or agriculture.
The species throughout its range inhabits arid and semiarid areas including plains and mountains, woodlands and pine forests, deserts, canyons and rocky vegetated foothills.
Geographical Range
Found in southeast California in Imperial, Riverside, and San Bernardino Counties.
There are a lot of old museum records for the species in the western Coachella Valley, as far west as a mile east of Cabazon, but due to all of the subsequent development and habitat loss there, it may no longer inhabitat that area.
Outside of California, the species ranges through much of Arizona, New Mexico, Oklahoma, and Texas, into Arkansas, and south into Mexico.
Possible occurance in San Diego County
Differentiating Crotalus atrox from Crotalus ruber is difficult where the ranges come in contact in San Diego and Riverside Counties. Snakes have been found in the San Diego County desert with the color and pattern of C. atrox, but their exact species has not been identified as far as I know. (Read more about this here.)
The California Department of Fish and Wildlife California Wildlife Habitat Relationships System range map for C. atrox(revised in 2012) shows the species
ranging west into San Diego County, overlapping the range of C. ruber, as well as throughout the Coachella Valley in Riverside County, where it could overlap the range of C. ruber in the north.
But the occurance of C. atrox in San Diego County is not confirmed. I have found two museum records for C. atrox from San Diego County - one from 1931 found at an undisclosed location, the other from "near Randalia" a place I can't find on the map. The validity of both of these records is questionable. In his 2006 field guide to San Diego County herps, Jeff Lemm mentions C. atrox in a list of taxa that are said to have been found in the county but remain unconfirmed. There are no records for the species from San Diego County reported to iNaturalist or the H.E.R.P. database (last searched 7/10/22).
Elevational Range
Generally found at elevations less than 1000 ft. (300 m).
Crotalus - Greek - krotalon - a rattle - refers to the rattle on the tail
atrox - Latin - atrox dark, fierce, savage - referring to the sometimes savage disposition of this species
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.
Flaxington, William C. Amphibians and Reptiles of California: Field Observations, Distribution, and Natural History. Fieldnotes Press, Anaheim, California, 2021.
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.
Taylor, Emily. California Snakes and How to Find Them. Heyday, Berkeley, California. 2024.
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.
Joseph Grinnell and Charles Lewis Camp. A Distributional List of the Amphibians and Reptiles of California. University of California Publications in Zoology Vol. 17, No. 10, pp. 127-208. July 11, 1917.
Conservation Status
The following conservation status listings for this animal are taken from the April 2024 State of California Special Animals List and the April 2024 Federally Listed Endangered and Threatened Animals of California list (unless indicated otherwise below.) Both lists are produced by multiple agencies every year, and sometimes more than once per year, so the conservation status listing information found below might not be from the most recent lists. To make sure you are seeing the most recent listings, go to this California Department of Fish and Wildlife web page where you can search for and download both lists: https://www.wildlife.ca.gov/Data/CNDDB/Plants-and-Animals.
A detailed explanation of the meaning of the status listing symbols can be found at the beginning of the two lists. For quick reference, I have included them on my Special Status Information page.
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 also go to the NatureServe and IUCN websites to check their rankings.
