Western Rattlesnake (Crotalus viridis). 



Description: Rattlesnakes belong to the pit-viper family, Crotalidae, which 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, the front of 

 which is 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 15-45 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. Females give birth to 4-21 young during the summer; the 

 young have the same color pattern as the adults (Hammerson 1982a) 



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. Rattlesnakes may den. 

 in large numbers, moving up to 10 miles out from the dens during the summer (Peterson, 

 pers. comm.) 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. 



Surveying: Walk-through surveys on warm sunny days, including rolling over rocks and logs is 

 probably the best method for determining relative numbers. Mark-recapture methods can be 

 done to determine more precise numbers. 



Status: The Western rattlesnake has not been found in the KNF but it is known from areas to the 

 east (Flathead Reservation) and south (Lolo NF). It would most likely be encountered in the 

 arid regions of the Fisher River and Fortine districts if at all present on the KNF. It is feared 

 and often needlessly killed due to its poisonous bite. The habit of denning at traditional sites 

 in large numbers makes rattlesnakes vulnerable to commercial collecting or simply killing by 

 fearful people. 



Montana Natural Heritage Program Rank: G5 S4. 



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