Crotalus

Crotalus
Timber rattlesnake, C. horridus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Reptilia
Order:	Squamata
Suborder:	Serpentes
Family:	Viperidae
Subfamily:	Crotalinae
Genus:	Crotalus Linnaeus, 1758
Synonyms
Crotalus Linnaeus, 1758 Crotalophorus Houttuyn, 1764 Caudisona Laurenti, 1768 Crotalinus Rafinesque, 1815 Crotalurus Rafinesque, 1820 Crotulurus Rafinesque, 1820 Uropsophus Wagler, 1830 Urocrotalon Fitzinger, 1843 Aploaspis Cope, 1867 Aechmophrys Coues In Wheeler, 1875 Haploaspis Cope, 1883 Paracrotalus Reuss, 1930

Common names: rattlesnakes, rattlers.

Crotalus is a genus of venomous pit vipers found only in the Americas from southern Canada to northern Argentina. The name is derived from the Greek word krotalon, which means "rattle" or "castanet", and refers to the rattle on the end of the tail which makes this group (genera Crotalus and Sistrurus) so distinctive. Currently, 32 species are recognized.

Description

Members of this genus range in size from only 50–60 cm (C. intermedius, C. pricei), to over 150 cm (C. adamanteus, C. atrox). In general, adult males are slightly larger than females. Compared to most snakes, they are heavy-bodied, although some African vipers are much thicker. Most forms are easily recognized by the characteristic rattle on the end of their tails, although a few island populations form exceptions to this rule: C. catalinensis has lost its rattle entirely, C. ruber lorenzoensis usually has no rattle, and both C. r. lucasensis and C. molossus estebanensis exhibit a tendency for rattle loss. The rattle may also be lacking in any species due to a congenital abnormality.

The rattle

The rattle consists of a series of loosely interlocking hollow shells, each of which was at one point the scale covering the tip of the tail. In most other snakes, the tail tip, or terminal spine, is cone-shaped, hardly any thicker than the rest of the skin, and is shed along with it at each successive molt. In this case, however, the end-scale, or "button", is much thicker and shaped like a bulb, with one or two annular constrictions to prevent it from falling off. Before each molt, a new button will have developed inside the last one and before the skin is shed, the tip of new button shrinks, thereby loosening the shell of the previous one. This process continues so the succession of molts produces an appendage consisting of a number of interlocking segments that make an audible noise when vibrated. Since younger specimens may shed three or four times in a year, every time adding a new segment to the rattle, the number of segments bears no relation to the age of the snake. In theory, the rattle could become very long indeed, but in practice, the older segments tend to wear out and fall off. How quickly this happens depends on the snake's environment, but end segments tend to break off after the rattle becomes about six or seven segments long; it is uncommon to find specimens with as many as a dozen segments. In captive specimens, however, as many as 29 segments have been found.

Geographic range

This genus is found in the Americas from southern Canada to northern Argentina.

Behavior

No species is considered aggressive; when threatened, most will retreat quickly. However, most species will defend themselves readily when cornered.

How far these snakes can strike has been controversial. Obviously this depends on the size of the animal, but other factors may also play a role, such as the species, the position of the body, and the degree of excitement. Additionally, there is the question of definition: from which point on the snake should a strike be measured: from the front, the middle, or the back of the anchor coil on the ground? Even if the length of the specimen is known, once it strikes, it is almost impossible to determine the limiting point reached by its head and the position of its body when the movement started. Therefore, it is not surprising that many conflicting statements can be found in the available literature about how far these snakes can strike. Estimates have been given that range from one-third of the body length, to half, three-quarters or even the full length of the animal. They rarely strike further than half of their body length, and almost never more than three-fourths, but that it is still not wise to trust such values if only because it is not possible to accurately judge the length of a coiled snake.

Feeding

Their diets generally consist of vertebrates, although many invertebrate species have also been consumed. Smaller species feed mainly on lizards, while larger species start by feeding on lizards as juveniles and then switch to preying mainly on mammals as adults. Prey items more frequently taken include rabbits, ground squirrels, tree squirrels, chipmunks, prairie dogs, gophers, and rats and mice, while those less frequently taken include birds, snakes, and amphibians. Cannibalism has been reported in a number of different species. Individuals that feed on rodents usually release their prey after a strike, and these snakes evidently can discriminate between trails left by prey that has or has not been envenomated.

Predators

For all species, the most significant threats come from people, but they also face many natural enemies. These include other snakes, such as king snakes (Lampropeltis), coachwhips (Masticophis), indigo snakes (Drymarchon) and racers (Coluber), birds, such as hawks, eagles, owls, roadrunners, and ravens, and mammals, such as coyotes, foxes, wildcats, badgers, skunks and pigs. Certain species of birds frequently prey on these snakes, but this is not without risk. Two cases were reported in which dead hawks found near venomous snakes had suffered hemorrhage and gangrenous necrosis due to snakebite.

Reproduction

This genus is ovoviviparous, giving birth to live young. The basic lifecycle of many Nearctic species has been known for quite some time. Females at an age of 26 months undergo vitellogenesis as they enter their third hibernation, mate the following spring, and give birth later in September or October.

A number of variations to this basic cycle occur. In North America, the females of some species store sperm in their oviducts for at least eight months, and the males (all species of which undergo spermatogenesis during the summer) store sperm in the vas deferens for at least a year. Thus, species that store sperm for a shorter duration mate in the spring and store sperm in the vas deferens, while those that do so for a longer duration mate in the fall and store sperm in the oviduct over the winter, after which fertilization occurs the following spring. In addition, species that occur further north, where it is colder during much of the year and the feeding and growing season is short, may reproduce only every other year or less. Those found in central and southern Mexico or the tropics have reproductive cycles that correspond mostly with the rainy season.

Venom

Two main hemotoxic effects are caused by rattlesnake venom. First, zinc-containing metalloproteases act upon capillary endothelial cells to cause platelet aggregation and hemorrhage. Second, the platelet antagonist crotalin creates a severe bleeding effect as it binds to the surface proteins, blocking aggregation. These two starkly different effects may seem counterproductive, but the effect should be profound. Firstly, endothelial-cell disruption causes lysis and internal bleeding. Then, as these hemorrhages increase, the natural thrombin response is hindered by the effect of crotalin increasing the toxic effect. Their observed hunting technique is a bite-and-release method, so a fast-acting toxin would be ideal. Assuming the natural median prey would be a small rodent such as a mouse, the bite would elicit a fear response, quickening heart rate and increasing blood pressure. This would speed the toxic effect, as well as spread the hemolytic and hemorrhagic effects.

Neurotoxic effects may also be caused by rattlesnake venom. These effects vary by species, and within species by population.

Species

Species	Taxon author	Subsp.*	Common name	Geographic range
C. adamanteus	Palisot de Beauvois, 1799	0	Eastern diamondback rattlesnake	The southeastern United States from southeastern North Carolina, south along the coastal plain through peninsular Florida to the Florida Keys, and west along the Gulf Coast through southern Mississippi to southeastern Louisiana
C. aquilus	Klauber, 1952	0	Querétaro dusky rattlesnake	The highlands of central Mexico: Guanajuato, Hidalgo, México, Michoacán, and San Luis Potosí
C. atrox	Baird & Girard, 1853	0	Western diamondback rattlesnake	The United States from central Arkansas and southeastern California, south into Mexico as far as northern Sinaloa, Hidalgo, and northern Veracruz, disjunct populations in southern Veracruz and southeastern Oaxaca
C. basiliscus	(Cope, 1864)	0	Mexican west coast rattlesnake	Western Mexico from southern Sonora to Michoacán
C. catalinensis	Cliff, 1954	0	Santa Catalina rattlesnake	Isla Santa Catalina in the Gulf of California (western Mexico)
C. cerastes	Hallowell, 1854	2	Sidewinder	The southwestern United States in the desert region of eastern California, southern Nevada, extreme southwestern Utah, and western Arizona, northwestern Mexico in western Sonora and eastern Baja California
C. durissus	Linnaeus, 1758	8	South American rattlesnake	All South American countries except Chile and Ecuador (although the various populations are disjunct), some islands in the Caribbean
C. enyo	(Cope, 1861)	2	Baja California rattlesnake	Western Mexico on the Baja California Peninsula from around Río San Telmo on the west coast and from opposite Isla Angel de la Guarda on the gulf coast, south to Cabo San Lucas, on the following islands in the Gulf of California: San Marcos, Carmen, San José, San Francisco, Partida del Sur, Espírita Santo, and Cerralvo, off the Pacific coast on the island of San Margarita
C. horridusT	Linnaeus, 1758	0	Timber rattlesnake	The eastern United States from southern Minnesota and southern Maine, south to east Texas and north Florida, in southern Canada in southern Ontario
C. intermedius	Troschel, 1865	2	Mexican small-headed rattlesnake	Central and southern Mexico, in southeastern Hidalgo, southern Tlaxcala, northeastern and south-central Puebla, west-central Veracruz, Oaxaca, and Guerrero
C. lannomi	W. Tanner, 1966	0	Autlán rattlesnake	Western Mexico in Jalisco
C. lepidus	(Kennicott, 1861)	3	Rock rattlesnake	The southwestern United States in Arizona, southern New Mexico, and southwestern Texas, south into north-central Mexico
C. mitchellii	(Cope, 1861)	4	Speckled rattlesnake	The southwestern United States in east-central and southern California, southwestern Nevada, extreme southwestern Utah, and western Arizona, in Mexico in most of Baja California, including Baja California Sur, on a number of islands in the Gulf of California and on Santa Margarita Island off the Pacific coast of Baja California Sur
C. molossus	Baird & Girard, 1853	3	Black-tailed rattlesnake	The southwestern United States in Arizona, New Mexico, and west and central Texas, in Mexico as far south as Oaxaca, in the Gulf of California on San Estéban Island and Tiburón Island
C. oreganus	Holbrook, 1840	6	Western rattlesnake	Southwestern Canada (southern British Columbia), south though much of the western half of the United States (Washington, Oregon, western and southern Idaho, California, Nevada, Utah, Arizona, and likely west-central New Mexico), and into northern Mexico (western Baja California (state) and the extreme north of Baja California Sur)
C. polystictus	(Cope, 1865)	0	Mexican lance-headed rattlesnake	Central Mexican Plateau, from southern Zacatecas and northeastern Colima east to east-central Veracruz
C. pricei	Van Denburgh, 1895	1	Twin-spotted rattlesnake	In the US from southeastern Arizona, and Mexico in northern Sonora southeast through Chihuahua, Durango, southeastern Coahuila and Nuevo León into Tamaulipas
C. pusillus	Klauber, 1952	0	Tancitaran dusky rattlesnake	West-central Mexico in southwestern and west-central Michoacán and adjacent Jalisco, probably also in northeastern Colima
C. ruber	Cope, 1892	2	Red diamond rattlesnake	The US in southwestern California, south through the Baja California Peninsula, except in the desert east of the Sierra de Juárez, also on a number of islands in the Gulf of California and two islands off the west coast of Baja California Sur
C. scutulatus	(Kennicott, 1861)	1	Mojave rattlesnake	The southwestern US in southern California, southern Nevada, extreme southwestern Utah, most of Arizona, southern New Mexico, and West Texas, and south into Mexico to southern Puebla
C. simus	Latreille In Sonnini & Latreille, 1801	2	Middle American rattlesnake	From Mexico in southwestern Michoacán on the Pacific coast, and Veracruz and the Yucatán Peninsula on the Atlantic coast, south through Belize, Guatemala, El Salvador, Honduras, and Nicaragua to west-central Costa Rica
C. stejnegeri	Dunn, 1919	0	Long-tailed rattlesnake	Western Mexico in eastern Sinaloa, western Durango, and probably northern Nayarit
C. tigris	Kennicott in Baird, 1859	0	Tiger rattlesnake	The southwestern US in south-central Arizona, and in northwestern Mexico in Sonora, on Isla Tiburón in the Gulf of California
C. tortugensis	Van Denburgh & Slevin, 1921	0	Tortuga Island diamond rattlesnake	Mexico, on Tortuga Island, in the Gulf of California]]
C. totonacus	Gloyd & Kauffeld, 1940	0	Totonacan rattlesnake	Northeastern Mexico from central Nuevo León through southern Tamaulipas, northern Veracruz, eastern San Luis Potosí, and northern Querétaro.
C. transversus	Taylor, 1944	0	Cross-banded mountain rattlesnake	Central Mexico in México and Morelos.
C. triseriatus	(Wagler, 1830)	1	Mexican dusky rattlesnake	Mexico, along the southern edge of the Mexican Plateau in the highlands of the Transverse Volcanic Cordillera, including the states of Nayarit, Jalisco, Michoacán, Morelos, México, Puebla, Tlaxcala, and Veracruz
C. viridis	(Rafinesque, 1818)	1	Prairie rattlesnake	Southern Canada (Alberta, Saskatchewan), south through the US (eastern Idaho, Montana, North Dakota, South Dakota, Wyoming, Nebraska, Colorado, Kansas, Oklahoma, Texas, New Mexico, extreme eastern Arizona), and into northern Mexico (northern Coahuila, northwestern Chihuahua)
C. willardi	Meek, 1905	4	Ridge-nosed rattlesnake	The US in southeastern Arizona and southwestern New Mexico, and northwestern Mexico in Sonora, Chihuahua, Durango, and Zacatecas

*) Not including the nominate subspecies
^T) Type species

See also

• List of crotaline species and subspecies
• Crotalus by common name
• Crotalus by taxonomic synonyms
• Crotalinae by common name
• Crotalinae by taxonomic synonyms
• Snakebite

Further reading

• Cope ED. 1867. On the Reptilia and Batrachia of the Sonoran province of the Nearctic region. Proceedings of the Academy of Natural Science of Philadelphia 18: 300-314[310].
• Cope ED. 1883. Notes on the geographical distribution of batrachia and reptilia in western North America. Proceedings of the Academy of Natural Science of Philadelphia 35: 10-35[13].
• Coues E. 1875. Synopsis of the Reptiles and Batrachians of Arizona; with Critical and Field Notes, and an Extensive Synonymy, p. 585-633.[609]. In Wheeler GM. 1875. Report Upon Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian. Volume V. Zoology: Reports Upon the Zoological Collections Obtained from Portions of Nevada, Utah, California, Colorado, New Mexico, and Arizona, During the Years 1871, 1872, 1873, and 1874. Government Printing Office, Washington, DC.
• Fitzinger LJFJ. 1843. Systema Reptilium. Fasciculus primus. Amblyglossae. Braumüller et Seidel, Wien: 106 pp.[29].
• Heckel JO, Sisson DC, Quist CF. 1994. Apparent fatal snakebite in three hawks. Journal of Wildlife Diseases 30(4): 616-619.
• Houttuyn, M. 1764. Natuurlyke historie of uitvoerige beschryving der dieren, planten en mineraalen, volgens het samenstel van den Heer Linnæus. Met naauwkeurige afbeeldingen. Eerste deels, zesde stuk. Dieren van beiderley leven. Amsterdam. 558 pp.[290].
• Hubbs, Brian and Brendan O'Connor. 2012. A Guide to the Rattlesnakes and other Venomous Serpents of the United States. Tricolor Books. Tempe, Arizona. 129 pp. ISBN 978-0-9754641-3-7.
• Keegan HL. 1944. Indigo snakes feeding upon poisonous snakes. Copeia 1944(1): 59.
• Klauber LM. 1927. Some observations on the rattlesnakes of the extreme southwest. Bull. Antivenin Inst. Am. 1(1): 7-21.
• Klauber LM. 1936. Key to the rattlesnakes with summary characteristics. Trans. San Diego Soc. Nat. Hist. 8(2): 185-276.
• Klauber LM. 1971. Classification, distribution and biology of the venomous snakes of northern Mexico, the United States and Canada: Crotalus and Sistrurus. pp. 115–156 In Bucherl W, Buckley E. 1971. Venomous animals and their venoms, vol. 2. Venomous vertebrates. Academic Press, New York.
• Klauber LM. 1972. Rattlesnakes: Their habits, life histories, and influence on mankind. 2nd edition. 2 Vols. Berkeley, CA: University of California Press.
• Laurenti JN. 1768. Specimen medicum, exhibens synopsin reptilium emendatum cum experimentis circa Venena et antidota reptilium Austriacorum. J.T. de Trattern, Wien. 214 pp.[92].
• Linnaeus C. 1758. Systema naturae per regna tria naturae secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. 10th ed. Vol. 1. Stockholm. 824 pp.[214].
• Rafinesque CS. 1815. Analyse de la nature ou tableau de l'univers et des corps organisés. Jean Barravecchia, Palermo. 224 pp. (Herpetol. section) pp. 73–78[77].
• Rafinesque CS. 1820. Annals of Nature, or Annual Synopsys of New Genera and Species of Animals and Plants Discovered in North America. Lexington. (22): 1-16.[5].
• Reuss T. 1930. Glasnik Zemaljskog Muzeja u Bosni I Hercegovini. Sveska za Prirodne Nauke. 42: 57-114[60, 88].
• Wagler J. 1830. Natürliches system der amphibien, mit vorangehender classification der Säugthiere und vögel. München, Stuttgart und Tübingen. vi, 354 pp.[176], 9 pls.

External links

• Crotalus at the Reptarium.cz Reptile Database. Accessed 3 August 2007.
• Crotalus at Herpbreeder.com. Accessed 26 September 2006.
• Sectioned rattle illustration at emilydamstra.com. Accessed 4 January 2007.
• Crotalus ruber Pictures of a crotalus in Baja California, Mexico.