Location: East San Diego County, CA
December 13, 2011 10:54 am
We found this bug on Sunday. He was hitting the windows and the door in the evening hours. We’ve seen these kind of bugs before, but only when it rains. It was damp and raining that day and 47 degrees. We are at an elevation of 4,000 ft., near the border of Mexico and California. We found it dead on a bucket the next morning.
While this is not a rare sighting, it is a somewhat unique sighting. Your beetle is a Rain Beetle, a member of the family Pleocomidae and the genus Pleocoma. This is a small family that is limited to coastal regions of the west coast of North America from Washington to Baja. This family is not known from any other parts of the world. There is work needed on the taxonomy of the genus and it would be nearly impossible for us to provide you an exact species identification. According to BugGuide, there are approximately 30 species identified. Many species have very limited ranges, due in large part to the morphology of the flightless female. One can only begin to ponder what conditions once existed that allowed the range expansion and genetic diversity that contributed to the evolution of distinct species where the female of the species is flightless and immobile. The grubs live underground, often at great depths, feeding on the roots of oaks and conifers according to BugGuide. You may find this May 18, 2009 Los Angeles Times article interesting.