|Western Diamondback Rattlesnake, Crotalus atrox Baird and Girard, 1853. Photographed in Cochise County, Arizona. Ranges from Arkansas to California and southward into Mexico. It occurs in northeast Baja, and extends southward to Hidalgo, the range may be discontinuous. Maximum size is controversial, snakes that reach 1.8 m are rare, a snake that was 2.34 m has been reported. Males are larger than females and engage in combat bouts. These are dangerous snakes and responsible for many bites, some of which result in human deaths. This fact, in addition to the the fact that livestock is frequently killed by this snake are often considered justification for the ever popular rattlesnake roundups that occur at various places in the western USA.|
|The Sidewinder, Crotalus cerastes Hallowell, 1854. Photographed in Cochise County Arizona. Ranges from central California and southern Nevada southward to Baja and Sonora. This is a snake of the desert, using dunes, creosote brush lands, mesquite brush lands, rocky terrain, and pinion-juniper woodland. Adult maximum size is 824 mm. Females give birth to 2-18 young in the summer. It is know to shelters in rodent burrows. Food is primarily rodents, lizards, and birds. The side to side movement is responsible for the common name, and is illustrated in the bottom photo. This appears to be the sister to the Mexican Lance Head Rattlesnake, C. polystictus.|
|South American Rattlesnake, Crotalus durissus Linnaeus 1758. Photograph of a captive snake. A widespread, polymorphic species that uses the drier habitats of South America. Maximum size possibly 1.8 m.|
The Timber Rattlesnake, Crotalus horridus Linnaeus, 1758. Photographed in central Wisconsin. Inhabits the forests of eastern North America from southern Maine and Minnesota southward to the Gulf Coasts of Texas and northern Florida. Adult maximum size is 1.89 m. This snake is dangerous to humans and its bite has resulted in human deaths. The Timber Rattlesnake shared an ancestor with the Mojave Rattlesnake, C. scutulatus; the Prairie Rattlesnake, C. viridis; and the Western Rattlesnake, C. oreganus.
|The Rock Rattlesnake, Crotalus lepidus (Kennicott, 1861). Photographed in West Texas (top) and Cochise County, New Mexico (bottom). Ranges from southern Arizona, New Mexico, and western Texas southward to Tamaulipas and Jalisco, Mexico. Adult maximum size 828 mm. Feeds on frogs, snakes, lizards and small mammals. Often associated with rock outcrops in grasslands, along streams, in forests. Females give birth to litters of 2-9 young.|
|Panamint Rattlesnake, Crotalus stephensi Klauber, 1930. Photographed in central California. Adults reach 1.3 m. This species inhabits the dry, higher, rocky canyons of the eastern Sierra Nevada Mountains to at least 7000 ft. This species was long considered a race of C. mitchelli, but recent molecular evidence suggests it is a distinct species (see Douglas et al. 2007. Copeia (4):920-932).|
|Southwestern Rattlesnake, Crotalus mitchelli pyrrhus (Cope, 1866). Photographed in San Diego Co., California. Speckled Rattlesnakes range from southern California southward into Baja California (Mexico). Adults may reach a maximum size of 1.32 m, but rarely are they more than one meter. The Southwestern Rattlesnake inhabit desert scrub, pinion-juniper woodland and is often associated with rock outcrops. Its diet includes small mammals, birds, and lizards. Females give birth to 2-12 young in the summer.|
|The Black Tailed Rattlesnake, Crotalus molossus Baird and Girard, 1853. Photographed in Cochise County, Arizona. Adult maximum length about 1.3 m. Ranges from northern Arizona, central New Mexico, and West Texas southward to Puebla and Oaxaca on the southern edge of the Mexican Plateau. Habitats range from pine-oak forests, oak savanna, and boreal forests to deserts, chaparral, and tropical deciduous forests. It is a montane snake, often associated with rock out crops and talus slopes. This is the sister to the Mexican West Coast Rattlesnake, C. molossus.|
|Twin Spotted Rattlesnake, Crotalus pricei Van Denburgh, 1895. Photographed in Cochise County, Arizona. Adult maximum size is 660 mm. It ranges from southeastern Arizona southward to Durango, and there are populations in Coahulia, Nuevo Leone, Tamaulipas, and San Luis Potosi. This is a montane snake that inhabits pine-oak forests and it is often associated with talus slopes. Its diet includes small mammals, birds and lizards.|
|The Mojave Rattlesnake, Crotalus scutulatus (Kennicott, 1861). Photographed in Presidio County, Texas. It ranges from southern Nevada, Southern California, Arizona, and West Texas southward into Mexico to Veracruz. Adult maximum size is about 1.37 m, most are less than one meter. It uses desert scrub, mesquite grasslands, and pine oak forests. It can also be found in agricultural areas, particularly along irrigation ditches. It eats a variety of small vertebrates, and its venom is quite toxic (and variable in its properties from one population to another). This species is the sister to the Prairie Rattlesnake, C. viridis.|
|The Tiger Rattlesnake, Crotalus tigris Kennicott, 1859. Photographed in southern Arizona. Maximum adult size about 910 mm. Ranges from central Arizona to southern Sonora, Mexico. There is also a population on Tiburon Island. It uses arid habitats including desert, mesquite, creosote, ocotillo, saguaro and palo verde, as well as oak forests. The diet includes lizards and mammals, and females give birth to small litters (1-6) of young. This snake is the sister to the Speckled Rattlesnake, C. mitchellii.|
|The Massasauga, Sistrurus catenatus (Rafinesque, 1818). Photographed in Monroe County, Wisconsin. They range from isolated populations in southeastern Canada southwest to southern Colorado, Texas, New Mexico, and Arizona, and it may have (or did have) populations in Mexico. Adults maximum length may reach one meter, but most specimens are less than 700 mm. Massasaugas feed on a variety of small vertebrates as well as some invertebrates. This species uses a variety of habitats, ranging from swamps to deserts. It is the sister to the Pygmy Rattlesnake, S. miliarius.|
|Pygmy Rattlesnake, Sistrurus miliarius (Linnaeus, 1766). Photographed in western Tennessee. Adult maximum size about 80 cm, most specimens much smaller. Uses wet habitats including floodplains, swamps, marshes, and forests from North Carolina to southern Florida and west to eastern Texas and Oklahoma. Food includes frogs, lizards and small mammals.|
Rattlesnakes are all American snakes and easily recognized due to the unique tail structure for which they are named. They probably evolved in the Mexican Mountains and dispersed north and south into the rest of North, Central, and South America. They show a strong tendency for dry habitats, but a few have adapted to wet forests. Most of them have large heads, slender forebodies, and heavy posterior bodies, and they range in size from the giant 2.5 m Eastern Diamondback to some of the dwarf species such as the Ridge Nosed Rattlesnake that is about 0.65 m at maximum. They tend to live long lives, mature slowly, and give birth to relatively small litters. Females show tendencies toward maternal care. At least some species have neonates that lure prey by wiggling their tails. The rattlesnakes are placed in two genera (sister groups), and they appear to be monophyletic, thus the rattle evolved only once. Some of these species are extremely dangerous, being aggressive, producing large amounts of very toxic venom. Other species have venom with relatively low toxicity.
In the 6th edition of the Origin of Species (1872) Charles Darwin made the following statement regarding rattlesnakes (page 162).