Saturday, December 8, 2012

The Ceruchus Stag Beetles of North America

We have three species of the stag beetle genus Ceruchus in the United States. They live under the bark of dead trees and are fairly small as stag beetles go (less than an inch long). they are often overlooked in the field because of their superficial resemblance to ground beetles or darkling beetles.  Open closer inspection, however, they are easily recognized as stag beetles with their lop-sided clubbed antennae. Another stag beetle genus that looks somewhat like Ceruchus is Platycerus (and related genera). Ceruchus can be separated from these groups by the relatively straight antennae. In Platycerus the first segment of the antennae connect to the remaining segments at a right angle (we call this arrangement geniculate).  In Ceruchus the segments follow each other without an angle. (Look closely at the image of C. punctatus. You can see the antenaae right at the base of the pronotum. The small segments arise from the end of the longer first segment that is just visible. Don't be confused by the curving of the segments near the club. This is typical of most stag beetles.)


One species (C. piceus) occures in southeastern Canada and throughout the northeastern part of the US. The color of this species is variable but is often has a bit more reddish color to it than the deep black which is typical of the genus.


Ceruchus striatus and C. punctatus occur in the western US. Their names are pretty diagnostic. Ceruchus striatus has clear and deep striae (the grooves down its back) whereas C. punctatus lacks the deep striae and has more obvious punctures.


Ceruchus striatus is fairly restricted to Washington, Oregon and parts of British Columbia (with some records in outlying areas). Ceruchus punctatus also occurs in these areas but can be found more commonly in California and Idaho.

1 comment:

beetlesinthebush said...

I've collected two specimens of C. piceus in Missouri over the years - as far as I can tell an unreported southwestern range extension for the species.