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Western Rattlesnake

(Crotalus viridis) 

Identification: Horny rattle or button on end of tail; numerous small scales on top of head; head much broader than neck; pit on each side of face between (but lower than) eye and nostril; upper side usually blotched; upper scales keeled; pupil vertically elongate (like a cat’s) in bright light; rarely greater than 100 cm total length (39 inches) in Colorado; in west-central and southwestern Colorado, adults rarely exceed 65 cm (26 inches) total length. VENOMOUS

Colorado Distribution: Throughout most of Colorado, except the high mountains, reaching an upper elevational limit of 7,500–9,500 feet in different areas of the state. Fairly common in many areas.    

Habitat: Virtually every terrestrial habitat within the broad geographic and elevational range; plains grassland, sandhills, semidesert shrubland, mountain shrubland, riparian zones, piñon-juniper woodland, and montane woodland; soils may be sandy to rocky; absent from perennially wet areas and high mountains; basically terrestrial, but sometimes climbs into vegetation or onto rocks or logs. Takes shelter in crevices, woodpiles, brushy vegetation, or mammal burrows. Hibernates in rodent burrows or in crevices in rock outcrops.    

Life History: Females give birth to their young between late August and early October. Typical food items include small mammals, lizards, occasional birds and spadefoot toads, and sometimes carrion. Prey are ambushed or obtained by active foraging.

Note: Rattlesnakes in west-central Colorado may be a distinct species. Under recent taxonomic proposals, populations in west-central Colorado (mainly Mesa, Delta, and Garfield counties) would be known as the Midget Faded Rattlesnake (Crotalus concolor, or C. oreganus), whereas those elsewhere in the state would be the Prairie Rattlesnake (Crotalus viridis).