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. 29 species are currently recognized.
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 the tail, 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 itself 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 that 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 that a succession of molts produces an appendage that consists of a number of interlocking segments that make an audible noise when vibrated. Since younger specimens may shed 3-4 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 6-7 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.
A highly controversial issue has always been how far these snakes can strike. Obviously this depends on the size of the animal, but other factors may also play a role, such as the species, the position the body is in 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 ⅓ of the body length, to ½, to ⅔, and even the full length of the animal. Klauber (1997) considered that they rarely strike further than ½ of their body length, and almost never more than ¾, 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.
The diet generally consists of vertebrates, although many invertebrate species have also been noted. 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. According to Klauber (1936, 1971, 1972), prey items more frequently taken include rabbits, ground squirrels, tree squirrels, chipmunks, prairie dogs, gophers, 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 will usually release their prey after a strike and there is evidence that these snakes can discriminate between trails left by prey that has and has not been envenomated.:506
For all species, the most significant threats come from people, but they also face many natural enemies. These include other snakes, such as kingsnakes (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 (Keegan, 1944; Klauber, 1927, 1936, 1971, 1972). Certain species of birds frequently prey on these snakes, but this is not without risk. Heckel et al. (1994) described two cases in which dead hawks were found near venomous snakes and had suffered hemorrhage and gangrenous necrosis. Their conclusion was that this was due to snakebite.:514
This genus is ovoviviparous, giving birth to live young. The basic life cycle of many Nearctic species has been known for quite some time. Klauber (1936) describes how females at an age of 26 months undergo vitellogenesis as they enter their third hibernation, mate the following spring and give birth a number of months later in September or October.:516
There are, however, a number of variations to this basic cycle. In North America, this is due to the ability of the females of some species to store sperm in the oviduct for at least eight months, and the males (all species of which undergo spermatogenesis during the summer) to 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.:516 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 that are found in central and southern Mexico or the tropics have reproductive cycles that correspond mostly with the rainy season.:519
There are two main hemotoxic effects caused by rattlesnake venom. First are the zinc-containing metalloproteases that act upon capillary endothelial cells. This effect can cause platelet aggregation and hemorrhage. Second is the platelet antagonist crotalin; this toxin creates a severe bleeding effect as it binds to the surface proteins blocking aggregation. These two starkly different effects may seem counter productive, however the effect should be profound. Firstly if the endothelial cells are disrupted this will cause a lysis effect and internal bleeding. Then as these hemorrhages increase, the natural thrombin response is hindered by the effect of crotalin increasing the toxic effect. Observed hunting technique is a bite and release method; so a fast acting toxin would be ideal. Assuming that 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 spreading the hemolytic and hemorrhagic effect.
|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 exist is 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. In northwestern Mexico in western Sonora and eastern Baja California.|
|C. durissus||Linnaeus, 1758||8||South American rattlesnake||Found in all South American countries except Chile and Ecuador, although the various populations are disjunct. Also occurs on 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. Also 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 it is also found 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. Also 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 northcentral Mexico.|
|C. mitchellii||(Cope, 1861)||4||speckled rattlesnake||The southwestern United States in eastcentral and southern California, southwestern Nevada, extreme southwestern Utah, and western Arizona. In Mexico in most of Baja California, including Baja California Sur. Also found 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. Also found 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 westcentral 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 United States 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||Westcentral Mexico in southwestern and westcentral Michoacán and adjacent Jalisco. Probably also in northeastern Colima.|
|C. ruber||Cope, 1892||2||red diamond rattlesnake||The United States in southwestern California, south through the Baja California Peninsula, except in the desert east of the Sierra de Juárez. Also found 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||Mohave rattlesnake||The southwestern United States in southern California, southern Nevada, extreme southwestern Utah, most of Arizona, southern New Mexico, and western 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 United States in south-central Arizona, and in northwestern Mexico in Sonora. Also found 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 off the coast of Baja California Sur.|
|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 the states of 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 United States (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 United States in southeastern Arizona and southwestern New Mexico, and northwestern Mexico in Sonora, Chihuahua, Durango, and Zacatecas.|
sound of a rattlesnake
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- List of crotaline species and subspecies
- Crotalus by common name
- Crotalus by taxonomic synonyms
- Crotalinae by common name
- Crotalinae by taxonomic synonyms
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