Rain Beetle

In ESNERR, Freshwater, Invertebrates and Insects, Slough Life, Staff Blog by Dave Feliz

Finally, we got some rain at the end of October. A day long shower soaked the Elkhorn Reserve thoroughly. I got up early Saturday morning to see if any amphibians were on the road. I did not see those critters but was surprised to see three strange looking beetles in one of our guzzlers. I posted a photo on my Facebook page and the animal was quickly identified by one of my Fish and Wildlife colleges as a Rain Beetle.

Well, with an interesting name like that, I thought it worth learning about these insects. Rain Beetles are found only in Western North America. They are all in the genus Pleocoma, the sole member of the family Plecomidae. There are 20 species known to occur in California.

Most of their lives are spent underground, where their various larval stages feed on roots of oak trees and other plants. It may take several years for these larvae to develop into adults. Rain events can trigger the emergence of adult male and female rain beetles. At this stage of their lives, they have no functioning mouth parts, so they are unable to feed. Males are able to fly and live only a few days. Females cannot fly and may live for months. The females release pheremones from the entrance of their burrow, hoping to attract a mate. Meanwhile, the males are flying low, searching for these females. Several males cluster around a female. She mates and goes into her burrow to lay her eggs. These eggs hatch about two months later. The male continues to seek out female partners and soon dies.

Apparently, when the males leave their burrows for their nuptial flights, they are attracted to lights and shiny pools of water. That is how they got into the guzzler Saturday morning.

You never know what you’ll find on the trail.

About the Author

Dave Feliz

Dave Feliz is the Reserve Manager at Elkhorn Slough National Estuarine Research Reserve