Beetles are the most commonly found insects at Ranch La Brea. Their remains (38,000 to 11,000 years old) represent 25 families. Many are extant and represent living species in the same area today. The biodiversity of insects found at Ranch La Brea is astounding (for a long list, see tarpits.org)
The La Brea beetles, like the fossil flies found there, were carrion feeders. The shiny wing covers are the predominant parts visible on the beetle fossils. They represent unaltered preservation by means of natural tar derived from seeps in the area.
The specimen figured below is a fossil water beetle (aka "fossil-tar bug")——which I tentatively identify as a Hydrophilus. This genus belongs to the carabid-beetle family. They apparently lived in thin-water layers overlying the sticky asphalt, and they attacked entrapped decaying animal carcasses. Eventually they became entrapped also in the asphalt (tar). The diversity and preservation of these insects and their different life-cycle stages are evidence that decaying large animals lay on the surface of the asphalt for up to five months. These insects indicate also that the climate in the area remained stable for thousands of years.
I have found these same bettles also at a Pleistocene tar pit near McKittrick, Kern Co., southern California.
La Brea "specimen" (just over an inch long)--this is a hand- painted plaster cast of an actual specimen.
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