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 mixed grass-coniferous forests. It is more likely 

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

 needlessly killed due to its poisonous bite. Rattlesnakes may den in large numbers, moving 

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

 most common in south-facing talus slopes. In Wyoming, it is found up to 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. In Colorado, females give birth to 4- 

 21 young during the summer (Hammerson 1982a). 



Surveying: A walk-through survey on a warm sunny day is probably the best method for 

 determining presence/absence; it is 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 HNF but is known from lower 

 elevation areas to the north, south, east and the valleys between the mountain ranges. It 

 would most likely be encountered at lower elevations in open habitats. The habit of denning 

 at traditional sites in large numbers makes rattlesnakes vulnerable to commercial collecting 

 or simply killing by fearfial people. Observations of Western Rattlesnakes should be reported 

 to document the presence of this species on the HNF; of particular interest would be 

 documentation of any denning sites located. 



Montana Natural Heritage Program Rank: G5 S4. 



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