California Rattlesnakes
Rattlesnakes are California's only venomous serpents, but they are also beautiful and fascinating reptiles. I'm not the type to pick them up all my viewing is at a very safe distance. Perhaps because I am always at a distance (or at least try to be!...), I've had trouble identifying some of them in the southeastern deserts where several species may occur. According to traditional taxonomy (e.g., Stebbins 2003, Crother et al. 2001) there are just six species, all in the genus Crotalus:
  • Western C. viridis
  • Western Diamondback C. atrox
  • Red Diamondback C. ruber
  • Sidewinder C. cerastes
  • Speckled C. mitchellii (left; Gilbert Pass, Inyo Co.)
  • Mojave C. scutulatus
But new taxonomic proposals, fueled by biochemical and mtDNA research, may change this system (see below).
Rattlesnakes seemingly appear when you least expect them. Take the hikers on this high Sierran trail (right). The last thing they are worried about up here at nearly 7000' elevation is a rattler in the trail, but there was a small Western Rattlesnake curled up right next to the main route (red arrow; close-up below). Over the years I've almost stepped on a half-dozen Western Rattlesnakes while hiking in Monterey County or in the Sierra; it always gives one an exceedingly strong jolt of adrenaline! 

[June 1997; Sequoia NP, Tulare Co.]
Western Rattlesnake (above; the subspecies C. v. oreganus, Northern Pacific Rattlesnake) is certainly the most widespread species in California, and is the only rattlesnake across most of northern California and in the coastal ranges north of Orange County. It is the only species with which I have lived from my childhood days in Lake Co. to my current home in Monterey County. Yet, in similar fashion to what is happening with the taxonomy of California slender salamanders, much of what I thought I knew is changing. New biochemical evidence suggest that there are two, three, or even seven (!) different species within what we have long called "Western Rattlesnake C. viridis" (e.g., Crother et al. 2001). Here is a short summary of the research that I found on line, quoting herpetologist Wolfgang Wüster:
Conventionally, the complex had been regarded as a single species, with 9 subspecies. Pook et al. (2000) carried out the first phylogeographic study of the complex, and suggested that three species might be recognisable, and Ashton & de Queiroz (2001) formally recognised an eastern species (C. viridis) and a western species (C. oreganus). Douglas et al. (2002) reviewed the systematics of the western rattlesnake (Crotalus viridis) complex, using a mtDNA phylogeographic approach, with special emphasis on the Colorado Plateau, and recognise seven species within the C. viridis complex:
  • Crotalus viridis  - Prairie rattlesnake (including the conventional subspecies viridis and nuntius, the latter being considered a synonym of C. viridis)
  • Crotalus abyssus - Grand Canyon rattlesnake
  • Crotalus cerberus - Arizona black rattlesnake
  • Crotalus concolor - Midget faded rattlesnake
  • Crotalus helleri - Southern Pacific rattlesnake (including the conventional subspecies caliginis, which is considered a synonym of helleri)
  • Crotalus lutosus - Great Basin rattlesnake
  • Crotalus oreganus - Northern Pacific rattlesnake
As in any complex group of snakes, it is likely that further research may yield further, different perspectives on the species limits within the C. viridis complex.

I have read the Pook et al. (2000) paper [available on line in pdf format] and find it fascinating stuff. They were able to reconstruct a phylogeny from mtDNA and, using a presumed mtDNA clock that has good concordance with known physiogeographic events (e.g., rise of the Andes; rise of the Sierra Nevada) can somewhat trace the history of these rattlesnakes from the Miocene. It seems that the trait of dwarfism arose independently twice, in C. v. nuntius ("Hopi Rattlesnake") and in C. concolor (Midget Faded Rattlesnake); the latter population also independently developed a Mohave-like highly lethal toxin. Certainly geologic events, like the formation of Grand Canyon, separated populations and led to developing species. However, unlike the more recent work by Douglas et al. (2002), they stopped short of going overboard on taxonomy and recommended that Western by split into three species: Prairie C. viridis; Arizona Black C. cerberus; and Western (the rest). Even though they stopped short of splitting the rattlers into 7 species, it is clear to me that there were influenced by the phylogenetic species concept (PSC) that has plagued bird taxonomy (e.g., they quote Cracraft, a primary proponent of this species concept in birds, liberally). I strongly suspect that the Douglas et al. (2002) work is grounded in the phylogenetic species concept. If that is true, I would hope that the more restrained "evolutionary species concept" on which Pook et al. (2000) rely better expresses the mainstream thought. although I fear it is a clone of the PSC. In any event, there is a lot going on with rattlesnake taxonomy!

I mentioned the problems I have had in the past trying to identify rattlesnakes in California. Because the colors of rattlesnakes can be so variably, depending on their habitat, Stebbins (1966, 1985, 2003) emphasizes scalation patterns that are damned near impossible to see in live snakes in the field, and hard to work with even in less-than-crystal-clear photos (i.e., in other words, my photos). Under I started putting together this page, and John Sullivan gently put me straight, I had misidentified and mislabeled the snakes shown above and right. They are, in fact, both different races of Speckled Rattlesnake C. mitchellii [as is the headline species at top of the page, also misidentified in the field]. Above is the beautiful Panamint Rattlesnake C. m. stephensi [photo May 1988 Willow Wash, Inyo Co.]; to the right is the much paler and less patterned Southwestern Speckled Rattlesnake C. m. pyrrhus [photo May 1985 Morongo Valley, San Bernardino Co.].

One small weakness of the maps in Stebbins' field guides is the lack of county borders, so it was hard to me to see what rattlers occur, for example, in Inyo County. Does Western Rattlesnake make it to the White Mts? Does Mojave Rattlesnake get to Death Valley? These questions were not clearly answered. I just did an on-line search of the specimens held at Museum of Vertebrate Zoology, U.C. Berkeley, and found that the only rattlesnakes in their collection from Inyo Co. are Speckled (the Panamint race) and Sidewinder. This makes things much easier.....

To the left is another photo of the same Panamint Rattler shown stretched out above. One thing I notice in this shot and in every other photo of Speckled Rattlesnake on this page and elsewhere on the web is that Speckled Rattlesnake has a really flat and triangular shaped head. Compare that head shape with the little Northern Pacific Rattlesnake (below) from Tulare County. The head of Western may be triangular but it is thick and jowly. I've noted this on a lot of other on-line photos also. Stebbins' field guides don't mention these shape difference but there is a very different jizz a concept birders will recognize to the heads of these, and presumably other, rattlesnakes. This character needs more work but might prove useful
One rattler that I have found easy to identify in southeastern California is Western Diamondback Rattlesnake [right and below, photos May 1998 near north end Salton Sea, Riverside Co.]. Its a BIG, thick-bodied, broad-headed rattler with conspicuous black-and-white rings before the rattle. I've read some surveys (e.g., Klauber 1972) that found the species to the the commonest snake (not just rattlesnake!) is some parts of southern Arizona (e.g., Organ Pipe Cactus NM). It is said to be an aggressive snake but, despite the look of the photo to the right, I've always kept a fair distance!

I have yet to see Red Diamondback or Mojave Rattlesnake in the state; it is interesting that Mojave is the rattler that has developed venom that is drop-for-drop some ten times more potent that ordinary rattlesnake venom. These and a wide host of interesting facts about rattlesnakes are found in the classic awork by Klauber (1972; this is the popularized, abridged version of his earlier multi-volume books). In researching this page, I also found the summaries and great photos in Mattison (1996) to be very helpful. That book not only has color photos of all U.S. species, but all the Neotropical species as well.

There are many on-line resources for rattlesnakes, but the "California herps" web site has photos of all of them in this State, with links to much additional information. More nice photos are on John Sullivan's "Wild Herps" web site.

Literature cited:

Ashton, K.G. & A. de Queiroz. 2001. Molecular Systematics of the western rattlesnake, Crotalus viridis (Viperidae), with comments on the utility of the D-Loop in phylogenetic studies of snakes. Molecular Phylogenetics & Evolution 21:176-189.

Crother, B.I., chair. 2001. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. Committee of Standard English and Scientific Names, Society for the Study of Amphibians and Reptiles, Herpetological Circular 29 (as supplemented in Herp. Review 32: 152-153).

Douglas, M. E., M.R. Douglas, G.W. Schuett, L.W. Porras & A.T. Holycross. 2002. Phylogeography of the western rattlesnake (Crotalus viridis) complex, with emphasis on the Colorado Plateau, pp. 11-50  in G.W. Schuett, M. Höggren, M. E. Douglas and H. W. Greene (eds.), Biology of the Vipers. Eagle Mountain Publ., Eagle Mountain, UT.

Klauber, L.M. 1972. Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind. Abridged ed. by K.H. McClung. Univ. of Calif. Press, Berkeley. Publ. for Zoological Soc., San Diego.

Mattison, C. 1996. Rattler! A Natural History of Rattlesnakes. Blandford, London.

Pook, C.E., W. Wüster & R.S. Thorpe. 2000. Historical biogeography of the western rattlesnake (Serpentes: Viperidae: Crotalus viridis), inferred from mitochondrial DNA sequence information. Molecular Phylogenetics & Evolution 15: 269-282.

Stebbins, R.C. 1966. A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.

Stebbins, R.C. 1985. A Field Guide to Western Reptiles and Amphibians. 2d ed. Houghton Mifflin, Boston.

Stebbins, R.C. 2003. A Field Guide to Western Reptiles and Amphibians. 3d ed. Houghton Mifflin, Boston.

PHOTOS: All photos © 2003 Don Roberson, all rights reserved. Specific details are in the main text above.

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