Crotalus ruber

Geographic Range

In southern California, Crotalus ruber (the Red Diamond Rattlesnake) can be found in San Bernadino, Los Angeles, Orange, Riverside, Imperial, and San Diego counties. In Baja California, it can be found from the U.S. border throughout the peninsula, and on the islands of Angel de la Guarda, Danzante, Monserrate, Pond, San Jose, San Lorenzo de Sur, San Marcos, Cedros, and Santa Margarita (Ernst and Ernst 2012).

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Red diamond rattlesnakes live in desert or coastal scrublands, chaparral, pine-oak woods, tropical deciduous forests, and occasionally in grasslands and other cultivated areas (Campbell and Lamar 2004, Ernst and Ernst 2012). They are most commonly found in areas with chaparral and sage scrub, low elevation, and high winter precipitation (Ernst and Ernst 2012). Particularly in the southern part of the range, Red Diamond Rattlesnakes prefer habitats with rocky outcroppings or heavy brush (Campbell and Lamar 2004). These are important for use as hibernacula (Brown et al. 2008). Studies suggest that Crotalus ruber prefers to avoid developed areas and are reluctant to cross roads (Thomson et al. 2016).

• Habitat Regions
• terrestrial terrestrial

• Terrestrial Biomes
• desert or dune desert or dune
• savanna or grassland savanna or grassland
• chaparral chaparral
• forest forest

Physical Description

Some authors recognize at least four subspecies; see Ernst and Ernst (2012) for descriptions of these. In the northern part of range these snakes are brick-red, reddish-gray, pinkish-brown, or tan dorsally. In southern Baja California, they are often yellowish-brown to olive-brown dorsally. Reddish-brown diamonds with a light border (which may be reduced on the lateral edges) are present on the dorsal side of the body, and may be separated by white or tan on the anterior half to two-thirds of the body. There may be 20-42 diamonds, though 33-35 is usual. A row of small, dark diamonds may be present laterally. Dorsal scales are keeled and pitted, excepting lateral rows 1-2. The most proximal rattle segment is black, and the tail has 2-7 black rings just anterior to the rattle (Ernst and Ernst 2012). In mainland populations, the rattle is well-developed, with up to 13 segments (Klauber 1982, Campbell and Lamar 2004). However, individuals from Isla San Lorenzo de Sur may lose rattle segments during shedding; about half of this population lack a rattle (Campbell and Lamar 2004). The venter has no markings, and is white to cream in color. The anal plate is undivided (Ernst and Ernst 2012).

The head is triangular, reddish, lacks a dorsal pattern, and has a diagonal dark stripe extending from the bottom edge of the eye to the corner of the mouth (Ernst and Ernst 2012, Thomson et al. 2016). The stripe has a light-colored border anteriorly; a posterior border may or may not be present (Ernst and Ernst 2012). Heat-sensing pits are located on either side of the head, between the nostrils and eyes. The neck is very thin (Thomson et al. 2016).

The confirmed maximum body length is 162.5 cm, though unconfirmed reports state the rattlesnakes may reach 190.5 cm. Island dwarfism has been observed; island snakes are usually less than 90 cm, while mainland snakes often exceed 100 cm (Ernst and Ernst 2012). Males are larger than females (Dugan and Hayes 2012).

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry
• venomous venomous

• Sexual Dimorphism
• male larger

Reproduction

Courtship and mating in the wild occur from March through May, though in captivity mating can occur year-around (Campbell and Lamar 2004, Ernst and Ernst 2012). Males will actively search for females, leading to an increased home range during the breeding season (Dugan et al. 2008). Following courtship, mating usually lasts from six to twelve hours, though it can sometimes last less than an hour or longer than twenty-two hours (Klauber 1982). Fertilization is accomplished via insertion of one (of two) hemipenes, as in all squamates. It is believed that sperm storage does not occur, though more research may be necessary (Brown et al. 2008).

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Gestation lasts from 141 to 190 days. Females give birth to litters of 3 to 20 young from July to December, usually in August or September (Campbell and Lamar 2004, Ernst and Ernst 2012). Juveniles resemble adults in patterning, though the coloration is duller and more grayish. Neonates measure 28 to 35 cm long at birth (Shupe 2011). Hybridization has occured with Crotalus helleri , but seem to be more common in captivity than in the wild (Klauber 1982).

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Females must invest considerable energy and resources in yolking eggs and carrying the developing young prior to birth. No post-birth parental care has been observed for Red Diamond Rattlesnakes; neonates have only been observed with their mother immediately after birth (Brown et al. 2008).

• Parental Investment
• no parental involvement
• precocial precocial
• pre-fertilization
  • provisioning
  • protecting
    • female

Lifespan/Longevity

An adult, wild-caught male lived an additional 19 years and 2 months as a captive. A zoo specimen lived 14 years 6 months.

Behavior

Crotalus ruber avoids severe heat and tends to be active at cooler temperatures. Thus, they are usually nocturnal from late spring through summer, and diurnal during cooler parts of the year. Most activity above ground occurs from April through June. The activity periods may vary depending on the surrounding environment; coastal populations tend to be more diurnal than desert populations (Campbell and Lamar 2004). These rattlesnakes typically hibernate from October or November through February or March (Ernst and Ernst 2012). Communal hibernacula may or may not be used (Brown et al. 2008, Dugan et al. 2008).

Red Diamond Rattlesnakes swim in freshwater lakes, reservoirs, and the Pacific Ocean, sometimes frightening fishermen (Klauber 1982, Ernst and Ernst 2012). However, it seems that they do not swim voluntarily, but are rather washed into rivers by heavy rainfall (Lillywhite 2014). These snakes are also capable of climbing into low bushes, cacti, and trees, where they may pursue arboreal prey such as birds and small mammals.

Male Crotalus ruber participate in ritualized combat "dances" which may last for longer than 15 minutes. These events occur most often during the breeding season. Combat is essentially a shoving match; the anterior portion of the body is raised and twisted around the opposing male (Campbell and Lamar 2004). The male which is successful in pinning the other to the ground is victorious. It was originally believed that the dances were involved in courtship; it is now thought that they are used in establishing dominance (Ernst and Ernst 2012).

Crotalus ruber generally have a peaceful disposition and are rarely aggressive (Klauber 1982). While some will rattle if approached, often they remain quiet or hide their heads. However, if provoked or cornered, they can present an animated defense, coiling, rattling, and striking (Ernst and Ernst 2012).

• Key Behaviors
• terricolous
• diurnal diurnal
• nocturnal nocturnal
• crepuscular crepuscular
• motile motile
• sedentary sedentary
• hibernation hibernation
• aestivation
• daily torpor
• solitary solitary
• territorial territorial
• dominance hierarchies dominance hierarchies

Home Range

The size of the home range varies by time of year. During the warmer seasons when they are more active, an individual may have a home range of 0.3 to 6.2 hectares. During the winter, the size of the home range will be far smaller, perhaps 100 to 2600 square meters. Males have larger home ranges than females and desert populations have larger ranges than coastal populations (Dugan et al. 2008).

Communication and Perception

Rattlesnakes as a group are famous for rattling their tails as a warning signal to potential threats (Greene 1997). The muscles in the tail are specialized to contract rapidly without fatigue. The shaker tail muscles can sustain a rate of 50 contractions per second for at least three hours, resulting in a sustained, high-frequency noise (Campbell and Lamar 2004). The rattle is not used outside of defensive purposes (Greene 1997). Though it has been suggested that rattles may be used for communication with conspecifics, the noises produced by rattles falls outside the hearing range of snakes (Lillywhite 2014).

In response to threats, Crotalus ruber individuals may also inflate the body and produce a long, sustained hiss. While hissing can serve as a basic warning signal, it is unlikely to encode any more complex information (Lillywhite 2014).

Crotalus ruber depends on visual, scent, and thermal cues to detect prey and potential mates (Ernst and Ernst 2012). The method of detection varies with time of day. Chemosensory methods are more common in the evening, perhaps to compensate for a lack of visual input (Barbour and Clark 2012). Detection of thermal and chemical cues is dependent on specialized anatomical structures and behaviors. Forward-facing heat pits are highly sensitive and are divided into two compartments. The inner chamber serves as a comparison to the outer chamber; since the inner chamber registers the ambient temperature of the air, if there is a thermal mismatch detected by the two chambers then the heat must be coming from a radiant object (Mattison 2007). Tongue-flicking is a commonly observed behavior which serves to transmit chemical cues to the vomeronasal organ. Mouth-gaping clears the vomeronasal organ, readying it to receive new input (Barbour and Clark 2012).

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• infrared/heat infrared/heat
• tactile tactile
• chemical chemical

Food Habits

Red diamond rattlesnakes are primarily ambush predators and hunt during both day and night (Barbour and Clark 2012, Dugan and Hayes 2012). A foraging site is chosen using chemical and thermo-visual cues (Barbour and Clark 2012). The snake remains motionless, striking when a prey item comes in range and injecting venom. Mammalian prey is immediately released to avoid injury to the snake, and followed by scent, using the vomeronasal organ. Eventually the prey item succumbs to the venom and is consumed by the rattlesnake (Barbour and Clark 2012, Ernst and Ernst 2012). Occasionally they will eat carrion (Dugan and Hayes 2012, Ernst and Ernst 2012). Gravid females may abstain from feeding (Dugan and Hayes 2012).

Mammalian prey items are most common. Red diamond rattlesnakes consume white-tailed antelope squirrels , agile kangaroo rats , desert kangaroo rats , Merriam's kangaroo rats , California voles , desert woodrats , southern grasshopper mice , California pocket mice , California mice , Canyon mice , cactus mice , western harvest mice , western spotted skunks , Audubon's cottontails , brush rabbits , and Botta's pocket gophers . Reptilian prey items are less common: tiger whiptails , Cape spinytail iguanas , desert spiny lizards , granite spiny lizards , and Central Baja spiny lizards . Birds, such as California towhees , are consumed only rarely (Dugan and Hayes, 2012).

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates

• Animal Foods
• birds
• mammals
• reptiles
• carrion carrion

Predation

Large adult red diamond rattlesnakes are likely only threatened by humans and occasional predation by coyotes . However, smaller individuals, especially juveniles, may also be consumed by kingsnakes , great horned owls , hawks , raccoons , badgers , striped skunks , western spotted skunks , bobcats , cougars , dogs , gray foxes , and kit foxes (Ernst and Ernst 2012).

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

In many habitats, red diamond rattlesnakes are top predators in their ecosystems. They have an important role in controlling prey populations, including many small mammals, lizards, and birds (Dugan and Hayes 2012, Corbit 2015). In addition to consuming woodrats , red diamond rattlesnakes sometimes use their nests as hibernacula (Brown et al. 2008). In some studies, a strong association has been observed between red diamond rattlesnakes, Opuntia cacti, and granite boulders. The boulders may provide hibernacula, while the cacti may provide protection from predators and be attractive to prey species (Brown et al. 2008).

Economic Importance for Humans: Positive

Rattlesnakes control small mammal populations, which can destroy crops and spread disease (Corbit 2015).

• Positive Impacts
• controls pest population

Economic Importance for Humans: Negative

Crotalus ruber is generally considered quite peaceful and has less toxic venom than many of the large American rattlesnakes (Campbell and Lamar 2004, Shupe 2013). However, bites may occur and can be quite dangerous. The venom contains proteolytic hemorrhagins, and it is estimated that 100 mg of venom would be fatal to a human. Symptoms of red diamond rattlesnake bites include swelling, pain, skin discoloration, hemorrhagic blebs, nausea/vomiting, coagulopathy, clinical bleeding, hemolysis, and necrosis (Campbell and Lamar 2004). Venom of adult rattlesnakes is 6 to 15 times more potent than juvenile venom (Mackessy 1985). If bitten, experts recommend seeking immediate medical attention. In southern California, Crotalus ruber accounts for 5.9% of bites caused by rattlesnakes; in the United States, there are only 5 to 7 deaths from all species of snakes combined each year. The probability of being bitten drastically increases if the snake is intentionally handled, or if drugs or alcohol have been consumed (Corbit 2015).

• Negative Impacts
• injures humans
  • bites or stings
  • venomous venomous

Conservation Status

Red diamond rattlesnakes are considered a Priority 3 Species of Special Concern in California, due to the decimation of coastal and sage scrub habitats for urban development (Dugan and Hayes 2012, Thomson et al. 2016). Crotalus ruber has been eliminated from approximately 20% of its historical range due to human development. Populations may be further threatened by persecution, road mortality, and shifts in fire regime and vegetation due to global climate change (Thomson et al. 2016).

Other Comments

Genetic and morphology studies show that Crotalus ruber is a member of the Crotalus atrox group of rattlesnakes (which includes Crotalus adamanteus , Crotalus atrox , Crotalus catalinensis , and Crotalus tortugensis ). This species is apparently most closely related to Crotalus catalinensis .

Additional Links

Encyclopedia of Life

Contributors

Amber Suto (author), Michigan State University, James Harding (editor), Michigan State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Barbour, M., R. Clark. 2012. Diel cycles in chemosensory behaviors of free-ranging rattlesnakes lying in wait for prey. Ethology , 118/5: 480-488.

Brown, T., J. Lemm, J. Montagne, J. Tracey, A. Alberts. 2008. Spatial ecology, habitat use, and survivorship of resident and translocated red diamond rattlesnakes ( C. ruber ). Pp. 377-394 in The Biology of Rattlesnakes . Loma Linda: Loma Linda University Press.

Campbell, J., W. Lamar. 2004. The Venomous Reptiles of the Western Hemisphere . Ithaca: Cornell University Press.

Corbit, A. 2015. The Dynamics of Human and Rattlesnake Conflict in Southern California. ProQuest Dissertations Publishing , 10032329.

Dugan, E., A. Figueroa, W. Hayes. 2008. 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 The Biology of Rattlesnakes . Loma Linda: Loma Linda University Press.

Dugan, E., W. Hayes. 2012. Diet and Feeding Ecology of the Red Diamond Rattlesnake, Crotalus ruber (Serpentes: Viperidae).. Herpetologica , 68: 203-217.

Ernst, C., E. Ernst. 2012. Venomous Reptiles of the United States, Canada, and Northern Mexico . Baltimore: The Johns Hopkins University Press.

Greene, H. 1997. Snakes: The Evolution of Mystery in Nature . Los Angeles: University of California Press, Ltd..

Klauber, L. 1982. Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind . Berkeley: University of California Press.

Lillywhite, H. 2014. How Snakes Work: Structure, Function, and Behavior of the World's Snakes . New York: Oxford University Press.

Mackessy, S. 1985. Fractionation of red diamond rattlesnake ( Crotalus ruber ruber ) venom: Protease, phosphodiesterase, L-amino acid oxidase activities and effects of metal ions and inhibitors on protease activity. Toxicon , 23/2: 337-340.

Mattison, C. 2007. The New Encyclopedia of Snakes . Princeton: Princeton University Press.

Shupe, S. 2011. U.S. Guide to Venomous Snakes and Their Mimics . New York: Skyhorse Publishing.

Shupe, S. 2013. Venomous Snakes of the World: A Manual for Use by U.S. Amphibious Forces . New York: Skyhorse Publishing, Inc..

Thomson, R., A. Wright, H. Shaffer. 2016. California Amphibian and Reptile Species of Special Concern . Oakland: University of California Press.