Adult, crawling on boulder at night,
San Diego County desert
Adult crossing a hiking trail in coastal San Diego County in the middle of the afternoon. You can see the tracks it made in the sand in the two pictures on the right.
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. Powell et al in A Key to Amphibians and Reptiles of the Continental United States and Canada 1998 say that the first infralabial scale is "usually" undivided on
C. atrox, which means that sometimes it can be divided. Does that mean that this snake from San Diego County is actually C. atrox? It's probably just not possible to know without DNA analysis.
The tail resembles that of the Western Diamond-backed Rattlesnake:
black and white rings, similar in width (with the white rings often appearing slightly wider) circle a thick tail just before the rattle. The ring adjacent to the rattle is usually black.
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.
Habitat
Habitat, San Diego County desert canyon
Habitat, rocky hillside, coastal
Riverside County
Habitat, Riverside County -
riparian desert foothills
Habitat, San Diego County desert oasis
Habitat, desert slope of
San Diego County mountains
Habitat, hillside coastal chaparral,
San Diego County
A large old Red Diamond Rattlesnake rattles on top of a boulder in coastal San Diego County.
A close view of a rattling Red Diamond Rattlesnake's tail.
A large adult Red Diamond Rattlesnake crawls up some large boulders at the edge of a desert wash in San Diego County. After trying to climb up past the top of the boulder, it crawled back down. Despite the bright lights, it did not appear to notice me and continued its nocturnal wandering.
A Red Diamond Rattlesnake crawls across the hot sand at mid day in San Diego County, then takes shelter between some rocks.
A Red Diamond Rattlesnake found on a desert road at night.
Listen to a rattlesnake rattling.
California State 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 are 30 - 65 inches in length ( 76 - 165 cm) typically 2 - 4.5 feet long.
Young are about 12 inches long.
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.
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.
29 scale rows.
Color and Pattern
Variable in ground color; pink, reddish-tan, reddish-brown or brick red.
Diamond-shaped blotches, usually with light edges, mark the back.
The underside is usually dull yellow and unmarked.
Black and white rings, similar in width, or with the white rings slightly wider, circle a thick tail just before the rattle.
The ring adjacent to the rattle is usually black.
Male/Female Differences
(Unlike most snake species, males of this species tend to be larger in body length than females.)
Young
Juveniles are duller in coloring than adults.
Newborn snakes do not have a rattle - just a single button which does not make a sound.
Similar Snakes
Similar to and easily confused with the Western Diamond-backed Rattlesnake - Crotalus atrox, but in California the ranges of these two snakes barely meet, and the Crotalus atrox in Calfornia does not typically show a red color phase.
Primarily nocturnal and crepuscular during periods of excessive daytime heat, but also active during daylight when the temperature is more moderate or when in the comparatively cooler shaded areas of boulder fields.
Not active during cooler periods in Winter.
Terrestrial, but may partially climb shrubs or trees.
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 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.
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.
Diet and Feeding
Eats small mammals, including ground squirrels, wood rats, and rabbits, lizards, and birds.
Prey is found when 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 prey by their warmth.
Long, hollow, movable fangs connected to venom glands inject a very toxic venom which quickly immobilizes the prey.
The snake can control the amount of venom injected and the fangs are replaced if broken.
Dugan and Hayes, 2012, found that this species specializes on mammalian prey, with terrestrial rodents the primary prey source. Wood rats were the most abundant prey species, followed by kangaroo rats, pocket mice, and deer mice. Coastal populations average longer in body size and eat a higher proportion of larger rodents than snakes from desert populations.
(Adult California Ground Squirrels are immune to rattlesnake venom and will intensely confront any snake they feel to be a threat.)
Rattlesnakes are ovoviviparous. 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.
Famales probably start bearing young at three years of age and breed annually. (Klauber, 1982)
Three to 20 young are born July through September. (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
Inhabits arid scrub, coastal chaparral, oak and pine woodlands, rocky grassland, cultivated areas.
On the desert slopes of the mountains, it ranges into rocky desert flats.
Geographical Range
Found in southwestern California, from the Morongo Valley west to the coast and south along the peninsular ranges to mid Baja California.
Possible overlaps with Crotalus atrox
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).
Notes on Taxonomy
Previously recognized as a subspecies of Crotalus ruber - Crotalus ruber ruber. Some taxonomists regard this snake as a subspecies of Crotalus exsul labelling it Crotalus exsul ruber.
Alternate and Previous Names (Synonyms)
Crotalus ruber - Red Diamond Rattlesnake (Stebbins & McGinnis 2012) Crotalus ruber ruber - Northern Red Rattlesnake (Stebbins 1985, 2003 ) Crotalus ruber ruber - Red Diamond Rattlesnake (Wright & Wright 1957, Stebbins 1966, Klauber 1982) Crotalus ruber - Red Diamond Rattlesnake (Stebbins 1954) Crotalus exsul - Red Rattlesnake (Crotalus atrox, part; Crotalus adamanteus ruber; Crotalus atrox ruber; Crotalus ruber. Red Diamond Rattlesnake; Western Diamond Rattlesnake, part) (Grinnell and Camp 1917) Crotalus ruber - Red Rattlesnake (Atsatt 1913) Crotalus ruber (Cope, 1892)
A CA Dept. of Fish and Game California Species of Special Concern, due to habitat loss in the coastal region. Protected from take with a sport fishing license.
Taxonomy
Family
Viperidae
Vipers
Crotalidae - Pitvipers
Genus
Crotalus
Rattlesnakes
Linnaeus, 1758
Species
ruber
Red Diamond Rattlesnake
Cope, 1892
Original Description
Crotalus ruber - Cope, 1892 - Proc. U.S. Natl. Mus., Vol. 14, p. 690
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.
Eric A. Dugan and William K. Hayes. Diet and Feeding Ecology of the Red Diamond Rattlesnake, Crotalus Ruber (Serpentes: Viperidae)
Herpetologica, 68(2), 2012, 203–217 E 2012 by The Herpetologists’ League, Inc.
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.
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.
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.
