Crotalus pusillus, or the Tancitaran Dusky Rattlesnake, is a venomous pit viper species found in west-central Mexico.

[3] Adult males may grow to more than 50 cm (20 in) in length, while females are smaller.

[4] 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.

[4] 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.