Mexican pigmy rattlesnake

Description

Sistrurus is a genus of venomous pit vipers in the subfamily Crotalinae of the family Viperidae. The genus is endemic to Canada, the United States, and Mexico. Its generic name is a Latinized form of the Greek word for "tail rattler" (seistrouros) and shares its root with the ancient Egyptian musical instrument, the sistrum, a type of rattle. Three species are currently recognized. Sistrurus species differ from the larger rattlesnakes of the genus Crotalus in a number of ways. They are smaller in size, but also their scalation is different: Sistrurus species have nine large head plates (same as Agkistrodon), whereas in Crotalus (and almost all other viperids), the head is mostly covered with a large number of smaller scales. Sistrurus species have a relatively small rattle that produces more of a high-pitched, buzzing sound than does a larger rattle, like that of Crotalus. Species of Sistrurus are found in Canada, the Western, Southern, and Midwestern United States, and isolated populations in southern and eastern Mexico.