Crotalus pusillus, or the Tancitaran Dusky Rattlesnake, is a venomous pit viper species found in west-central Mexico. No subspecies are currently recognized.
Description Adult males may grow to more than in length, while females are smaller. The largest recorded length for a specimen was .Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. .
Behavior Campbell and Lamar (2004) found this species only to be active during the day. Within its range, night temperatures are low and seem to restrict its activity.
Geographic range It is found in west-central Mexico in the Sierra de Coalcomán of southwestern Michoacán, the Transverse Volcanic Cordillera of west-central Michoacán, and in adjacent Jalisco. It is probably also found in northeastern Colima. Its type locality is reported as "Tancítaro, Michoacán, Mexico, altitude 5,000 ft" (5,000 ft = 1,524 m). It occurs at elevations between .
Conservation status This species is classified as Endangered on the IUCN Red List of Threatened Species. The population trend was unknown when assessed in 2007.
References
Further reading Klauber, L.M. 1952. Taxonomic studies on rattlesnakes of Mainland Mexico. Bull. Zool. Soc. San Diego 26:1-143.
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