False Bombardier Beetle - Chlaenius cumatilis
Anza-Borrego Desert State Park, San Diego County, California, USA
March 12, 2006
Size: BL 13 mm
This beetle was found creekside under a good-sized rock in Borrego Palm Canyon.
It is very possibly Chlaenius (Chlaenius) cumatilis based on the following:
First, according to Michael Caterino, "it looks like the common beetle generally called cumatilis". . . although he does not know if that is the right identification.
Then I tried to key it out, though keys are usually too technical. I used R. T. Bell's "Revision of the genus Chlaenius Bonelli (Coleoptera, Carabidae) in North America, Misc. publications of the Ent. Soc of America, 1: 98-166., 1960.
The subgenus seems to be Chlaenius, with the key stating "Third segment of antenna elongate, longer than first and second combined, and longer than fourth segment." This is true for this individual.
There are six species groups in this subgenus. The Cursor group seemed most likely. The other groups did not seem to fit in one detail or another.
In the key to the Cursor Group, the two keys to cumatilis are: 1a. Elytral entirely green or blue, and 2a. Pronotum opaque; abdomen entirely glabrous. (versus, Pronotum shining; abdomen pubescent).
Under the species C (C.) cumatilis, the type locality is San Diego, Ca. Measurements are: Total length 11.6-13.6 mm. Appendages are orange-brown to red-brown. Its range includes several sites in San Diego County including "Borego" ( our locale) as well as Palm Canyon and Palm Springs (which could be in San Diego or Riverside Counties), similar habitats to where we found it.
So my identification of species is really based on preponderance of the evidence.