Western Rattlesnake (Crotalus viridis) 



Description: Rattlesnakes have a heat-sensing pit located between the nostril and the eye. The 

 fangs are hollow and hinged, allowing them to be folded back against the roof of the mouth. 

 The head is triangular in shape and blunt-nosed. The eyes are slightly elevated. There are 

 several white lines which run along the side of the head. Adult Western Rattlesnakes have a 

 narrow neck but a stout body with total length ranging from 15-60 inches. The dorsal 

 background color varies from pale green to brown with a series of brown or black blotches 

 edged with a dark and then light line extending the length of the body. The blotches often 

 merge into rings on the tail. There are also blotches on the sides of the body. The ventral 

 side is pale yellow to white and without blotches. The scales are keeled. The tail ends in a 

 rattle which helps to warn potential predators of the snake's presence. The young have the 

 same color pattern, but are brighter in color than adults. 



Similar species: No other snake in Montana has rattles, but see Racer, Gopher Snake and 

 Western Hognose Snake which may have similar color patterns. 



Habitat and Habits: The Western Rattlesnake is an inhabitant of more open and arid country, but 

 it is also found in Ponderosa pine stands or mi.xed-grass coniferous forests. It is more likely 

 to be encountered on south-facing slopes and areas of rock outcrops. It is feared due to its 

 poisonous bite and therefore often needlessly killed. Rattlesnakes may den in large numbers, 

 moving up to 7 miles out from the dens during the sununer (Peterson, pers. comm.); den sites 

 are most common in south-facing talus slopes. In Wyoming, it is found at elevations of over 

 8500 feet (Baxter and Stone 1985). Rattlesnakes prey on a variety of animals including mice, 

 ground squirrels, rabbits, amphibians, and other snakes. Females give birth to 4-21 young in 

 Colorado during the summer (Hammerson 1982a). 



Surveying: Walk-through surveys on warm sunny days are probably among the best methods for 

 determining presence/absence; easiest to find near den sites in spring and fall. Funnel traps 

 and night driving are both effective techniques. Mark-recapture methods can be used to 

 determine more precise numbers. 



Status: The Western Rattlesnake was not been found in the Sioux-CNF during our surveys but is 

 known historically from the Long Pines (Appendix 4), and Visher (1914) considered it 

 locally common in Harding County. The habit of denning at traditional sites in large 

 numbers makes rattlesnakes vulnerable to commercial collecting or simply killing by fearful 

 people. Observations of Western Rattlesnakes should be reported to document the presence 

 of this species on other Units of the Sioux-CNF; of particular interest would be 

 documentation of any denning sites located. 



Montana Natural Heritage Program Rank: G5 S4. 



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