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False Bombardier Beetle - Chlaenius cumatilis

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.

Moved to species page. Sorry about my misspelling "cumitilis" below.

"preponderance of the evidence"
That's how most identifications are made.

Identifiing insects
There are two problems with identifying these insects. The first is that they are from photographs, and even the best photo usually lacks some detail that is called for in a key. The second problem is that even when there is a specimen available to key out, the terminology and so the keys are too technically difficult for the non-specialist to have a lot of confidence in the end result. I think it's important for me to try to key out a species, for it is a real learning experience, but I'm well aware of my own limitations. Here, BugGuide is a fabulous source and I'm grateful to all who have helped me with identifications.

I bet you that the next time you pass
a Chlaenius specimen through Bell's key it will be easier. And so it goes - you learn new terminology and how to recognize the structures referenced in the key. With experience you will even be able to apply a new species key for the first time to a genus unfamiliar to you and still feel fairly comfortable in where the "treasure map" takes you. I like to thinks of a taxonomic key as treasure map whose reward is a great deal of satisfaction at the species marked "X".

I hope you are right
Keys are wonderful when they work out, because knowing the species gives us the most available information possible about our bug, automatically a favorite bug after working it through the keys!

I am right, if ...
you also have access to a good stereo microscope (at least 30X) and a good light source to examine specimens. Photographs alone won't be sufficient in many cases.

C. cumitilis
Looks like C. cumitilis I have seen in AZ, but not sure all what is in CA.

Agree that best image fit is Chlaenius cumitilis
which compares well to the type specimen. US range includes only AZ and CA. Also note coarse punctures sparsely distributed atop pronotum, the main character that leads to the "cursor group". Lynn, the extra detail you presented is very helpful. I only wish that if a single photo is submitted, then it would be best a perpendicular dorsal view for best chance of accurate identification from image.

Chlaenius cumitilis
Thanks you all for your comments and identifications. I'm really happy that you agree it may well be C. cumitilis. Keys are not made for the non-specialist! Do you think it is safe to move this to C. cumitilis?

for practical purposes of BugGuide, your data and image says nothing against Chlaenius cumitilis and so a move to the species page is appropriate in my opinion.

Chlaenius cumitilis
This is a new species to BugGuide. As such, I can't move it.

Lynn, thanks for posting this image... response to my request. It's great to see a clearer image and your observations and notes are also much appreciated. I really hope that someone with some expertise in this area is able to corroborate your suspicions or possibly even confirm the ID!

Thank you for suggesting it!
I would not have posted without your suggestion. It's great to have my suspicions considered valid.

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