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. There are several white lines which run along 

 the side of the head. Adult Western Rattlesnakes 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 aduhs. 



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 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 summer (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 in Colorado give birth to 4- 

 21 live young during the summer (Hammerson 1982a). In 1998, this species was seen 

 between 4 May and 22 July (Appendix 4). In 1995 in Carbon County, they were reported 

 between 2 July (a juvenile, 39 cm total length) and 1 1 September. Most records from the 

 Ashland and Sioux districts, Custer National Forest are from June and July (Reichel 1995, 

 Hendricks and Reichel 1996), but one was reported on 27 September 1995. 



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

 determining presence/absence. This species is easiest to find near den sites in spring and fall. 

 Funnel traps and night driving are both efi'ective techniques. Snakes are often encountered 

 sunning on roads in the morning. Mark-recapture methods can be used to determine more 

 precise numbers. 



Status: The Western Rattlesnake is more common in eastern Montana than MTNHP records 

 indicate. Most encounters with this species do not get reported. In 1998, the species was 

 recorded 4 times from 4 counties (Appendix 4), and 4 more times from Carbon County in 

 1995. Other 1998 reports are from Stillwater and Yellowstone counties. The species is 

 widespread across the eastern part of the state. Nevertheless, there are no records whatsoever 

 from the 3 northeastern counties north of the Missouri River, and no records from north of 

 the river in adjacent North Dakota (Wheeler and Wheeler 1966) or Saskatchewan (Secoy and 

 Vincent 1976). The habit of denning at traditional sites in large numbers makes rattlesnakes 

 vulnerable to commercial collecting or simply killing by fearfiil people. Observations of 

 Western Rattlesnakes should be reported to document the presence of this species elsewhere 

 and to fill in distribution gaps, of particular interest would be documentation of any denning 

 sites located. 



Montana Natural Heritage Program rank: G5 S4. 



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