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Differences Between

Western Diamond-backed Rattlesnake - Crotalus atrox
&
Red Diamond Rattlesnake - Crotalus ruber

 






Northern Mohave Rattlesnake Range MapRed Diamond Rattlesnake - Crotalus ruber

Western Diamond-backed Rattlesnake Habitat range mapWestern Diamond-backed Rattlesnake - Crotalus atrox




observation link

 
There is a slight overlap in range between these two species of rattlesnakes in Imperial County and there may also be an overlap in Riverside County. The tail rings and head appearance is similar for both species and can't be used to distinguish the species, but one of the characteristics below might help.
 
Color

Generally C. ruber has a reddish appearance while C. atrox has a more gray or brown appearance, but this is not always definitive.
Red Diamond Rattlesnake - Crotalus ruber
Red Diamond Rattlesnake Red Diamond Rattlesnake Red Diamond Rattlesnake
San Diego County desert Western Imperial County desert Western Imperial County desert
     
Western Diamond-backed Rattlesnake - Crotalus atrox
Western Diamond-backed Rattlesnake Western Diamond-backed Rattlesnake Western Diamond-backed Rattlesnake
Riverside county © William Flaxington
Riverside County © Patrick Briggs Riverside County © Chad Lane
 
Conspicuous Dark Dots in Body Blotches
The Western Diamond-backed Rattlesnake has conspicuous dark dots in the body blotches, while the Red Diamond Rattlesnake does not.

This characteristic is mentioned in Stebbins, 2003, however the dark dots in the body blotches of the Western Diamond-backed Rattlesnake is not always obvious to me and some Red Diamond Rattlesnakes seem to have dark dots. But when they are present, the dark dots in the Red Diamond are usually not as dark as those in the Western Diamond-backed, and they are often missing, so this might be the best characteristic to use to separate the two species in the field.

Red Diamond Rattlesnake - Crotalus ruber
Western Diamond-backed Rattlesnake Western Diamond-backed Rattlesnake Western Diamond-backed Rattlesnake
Eastern San Diego County desert
(This snake shows some fairly dark scales in the body blotches.)
Western Imperial County Western Imperial County
 
Western Diamond-backed Rattlesnake - Crotalus atrox
Western Diamond-backed Rattlesnake Western Diamond-backed Rattlesnake Western Diamond-backed Rattlesnake
Riverside County © Chad Lane Riverside County © Patrick Briggs Calexico, Imperial County
© Tom Millington
     
First Infralabial Scales  -  Divided or Undivided

The best characteristic I can find to distinguish these two species is the makeup of the first infralabial scales, but they are not easy to see in the field. In order to examine them the snake probably needs to be in hand in order look at the front of the underside of the chin. This is not always possible and can be dangerous, so it is not recommended except for experienced venomous snake handlers.

The first infralabial scale:
- usually divided transversely on C. ruber
- usually undivided on C. atrox
(Click on a diagram for a larger view.)
 
 
Rattlesnake References


Robert Powell, Joseph T. Collins, and Errol D. Hooper, Jr.
A Key to Amphibians and Reptiles of the Continental United States and Canada.
© 1998 by the University Press of Kansas.

Chester J. Stojanovich and Margaret A. Parsons. Snakes: Pictorial Key to Venomous Species in United States

Klauber, Laurence M. Rattlesnakes. University of California Press. (Abridged from the 1956 two volume Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind.) University of California Press, 1982.

Stebbins, Robert C., and McGinnis, Samuel M.  Field Guide to Amphibians and Reptiles of California: Revised Edition (California Natural History Guides) University of California Press, 2012.

Stebbins, Robert C. California Amphibians and Reptiles. The University of California Press, 1972.

Hubbs, Brian R., & Brendan O'Connor. A Guide to the Rattlesnakes and other Venomous Serpents of the United States. Tricolor Books, 2011.

Bartlett, R. D. & Patricia P. Bartlett. Guide and Reference to the Snakes of Western North America (North of Mexico) and Hawaii. University Press of Florida, 2009.



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