Crotalus is a genus of venomouspitvipers 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 that make this group 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 addition, 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.
Found in the Americas from southern Canada to northern Argentina.
None are considered aggressive. In fact, when threatened most will retreat quickly. However, most species will defend themselves readily when cornered.
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.
This genus is viviparous, giving birth to live young.
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 though southern Mississippi to southeastern Louisiana.
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.
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.
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.
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. 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.
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).
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.
From Mexico in southwestern Michoacán on the Pacific coast, and Veracruz and the Yucatan Peninsula on the Atlantic coast, south through Belize, Guatemala, El Salvador, Honduras and Nicaragua to west-central Costa Rica.
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.
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).
^ abcde McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. ISBN 1-893777-00-6 (series). ISBN 1-893777-01-4 (volume).
^ Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates (7th printing, 1985). 1105 pp. ISBN 0-8014-0463-0.
^ abcdefghij Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.
^ abcdCrotalus (TSN 174305). Integrated Taxonomic Information System. Accessed on 23 August 2007.
^ abc Klauber LM. 1997. Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. Second Edition. First published in 1956, 1972. University of California Press, Berkeley. ISBN 0-520-21056-5.
^ Parker HW, Grandison AGC. 1977. Snakes -- a natural history. Second Edition. British Museum (Natural History) and Cornell University Press. 108 pp. 16 plates. LCCCN 76-54625. ISBN 0-8014-1095-9 (cloth), ISBN 0-8014-9164-9 (paper).
^ Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp. ISBN 0-448-11856-4.