The other genus, Sistrurus, includes the pigmy rattlesnakes and massasaugas, which normally have nine large plate-like scales on their heads and slender tails with small rattles. They are considered to be more primitive than the true rattlesnakes and may represent a "side path" on the evolutionary road from moccasin-like ancestors to the rattlesnakes.
This group is represented in the southwestern U.S. by the desert massasauga (Sistrurus catenatus edwardsi). This species enters Arizona in the southeastern portion of the state and inhabits low-lying damp areas in the desert-grasslands. Its range may have been reduced in historic times due to overgrazing.
The region encompassed by Arizona, Sonora, Baja California, and the Gulf of California islands is exceedingly rich in rattlesnake diversity with at least thirty-six subspecies represented. Seventeen are found in Arizona alone, making it the rattlesnake capital of the United States. The striking variation in topography and ecosystems largely accounts for this diversity.
Generally speaking, the rattlesnakes of Arizona might be grouped into three categories based upon altitudinal and habitat preferences, e.g., the desert grassland species, the foothill species and the Upper Sonoran-montane species. Several species overlap these categories to some extent.
| western diamondback
rattlesnake (Crotalus atrox) |
Mohave rattlesnake (Crotalus scutulatus) |
sidewinder
(Crotalus cerastes) |
| tiger rattlesnake
(Crotalus tigris) |
black-tailed
rattlesnake
(Crotalus molossus) |
western rattlesnake
complex
(Crotalus viridis) |
| banded rock rattlesnake (Crotalus lepidus klauberi) |
twin-spotted rattlesnake (Crotalus pricei) |
ridge-nosed rattlesnake (Crotalus willardi willardi) |
| Montane Rattlesnakes | Rattlesnake Conservation | desert-grassland massasauga
(Sistrurus catenatus edwardsi) |