Bumble flower beetles: Not your typical grub
“Little brown bumble bees” buzzing around low to the ground are actually beetles that pollinate flowers and decompose organic matter.
On a farm visit this week for Michigan State University Extension, I was asked to look at a bee infestation around the base of a tree that flared up when a mower came through. Much to my surprise and delight they were not angry wasps or bees, but bumble flower beetles (Euphoria inda).
I had just seen bumble flower beetles in a garden in Cincinnati two weeks previous, visiting flowers and buzzing around the ivy. These beetles are related to other white grub beetles, such as June beetles, Japanese beetles and chafer beetles, but are not a pest of major concern. They are furry with yellowish brown hairs on the front of their backs and undersides, with a mottled gray and brown shell. They are roughly the diameter of a nickel and are unique among beetles in that they do not lift their hard protective shell when flying. This lends them the appearance of a flying rock or clod of dirt.
As grubs, these beetles feed on dead and decaying plant matter. Once they molt into adults, they exhibit very convincing bumble bee behavior and sounds as they search for pollen, nectar, plant sap, fruit juices and mates. Once mated, they lay their eggs around dying vegetation. They can sometimes be found feeding on secondary injuries to trees and herbaceous plants that cause sap flows, and also on over-ripe, damaged or dying fruit and vegetation.
Typically, they are not of economic consequence in crops or turf, and live more of a gleaning lifestyle, taking advantage of damage done by other causes. They do not transfer any known diseases.
The grower was pleased that he did not have to treat and to know that these beetles were likely assisting with nutrient turnover and pollination on his property, and not hurting.