This small rattlesnake, averaging about 26 inches long, is endemic to Guerrero, Mexico, in the Sierra Madre del Sur. Its diet consists of lizards, small mammals, and sometimes insects. In 2018, the subspecies under C. ravus were all elevated to species status, including the Guerreran pygmy rattlesnake. This divergence is based on newfound phylogenetic evidence.

The specific epithet "exiguus" is Latin for "small" referring to its relatively smaller rattle compared to closely related rattlesnake species.

The Guerreran pygmy rattlesnake has a hemotoxic venom high in Phospholipidase A2. However, bites on humans are rare; and it is unknown how this venom affects the wide variety of prey consumed by this species.