Californias mountains were lower and gentler then, posing less of a barrier to an animal whose only means of expanding its range is by chewing its way through the soil. Even today, two million years after Californias inland seas dried up, the waters effect on the beetles distribution is striking. Wherever water covered the state then including much of the San Joaquin Valley and northern portions of the Coast Ranges there are no Pleocoma now. Rain beetles are scarabs, that family of large-bodied beetles that includes the dung beetle, an insect held sacred by ancient Egyptians. Pleocoma translates from Latin and Greek as many hairs, and rain beetles are indeed hairy.
Long bristles cover their undersides, hang from their legs, and line their wing covers.
Adult beetles are broadly oval and shiny, varying in color from dark honey to mahogany to black. Perhaps my Nevada County neighbors would have felt more kindly toward the beetles that invaded their yards last year if theyd known that Pleocoma lead a long but from a human point of view, at least miserable life. Only a handful of insects are known to live longer. Unlike most other soil-dwelling grubs, which dig with their six thoracic feet, Pleocoma use powerful mandibles to move through the soil one bite at a time, pausing between every couple of mouthfuls to deposit the excavated dirt into the tunnel behind them, deftly maneuvering the clods with their mouthparts and legs. On a good day, a grub in top form can move two to three inches through hard-packed soil.