Green June Beetles (Cotinis nitida, family Scarabaeidae) are practicing their annual terrorizing of backyard gardeners, golfers, sunbathers, small pets, etc., as they buzz golf courses and lawns. Despite the "June" in their common name, these beetles appear on the scene in July in Ohio.
The large, metallic green beetles tend to emerge en masse. Their large size, coupled with an audible "buzzing" sound and low-level flight plan; cruising at about 2 – 3' above the ground, may induce mild panic in the uninitiated. In fact, as I discovered in my (misspent) youth, the attractive beetles have great entertainment value. Tying a string to a hind leg of one of these powerful flyers turned the beetle into a drone before there were drones.
Unlike many of their scarab cousins, I've never seen green June Beetles feeding on plant leaves and there's a good reason. The adults have spatulate mandibles adapted to a “soft diet.” They can damage ripened fruit but will also feed on oozing sap and other plant juices. About all they could do with a leaf would be to tickle it a bit.
The beetles seek turfgrass with high levels of organic matter (e.g. thatch) in which to lay eggs. It has been speculated that this attraction to decomposing organic matter explains why large numbers of adults will cruise above certain lawns while ignoring neighboring lawns.
Unlike other Scarab beetle larvae found in turfgrass, green June beetle grubs burrow 10 – 12" vertically into the soil and they remain closely associated with these burrows. The grubs exit their burrows at night to feed on thatch and other organic matter.
This is one of the largest and strangest white grubs you'll ever see in Ohio. First, the mature grubs are huge measuring well over 1" in length. They look like white grubs on steroids.
Second, the grubs practice an unusual mode of locomotion: they crawl along on their backs in an undulating motion. Their rolling motion causes them to superficially resemble caterpillars. Their legs are smaller than those of other white grubs in relation to the size of their bodies. Some have speculated their leg-size is an adaptation to life in a burrow while their unusual style of crawling reconciles having small legs. Regardless, the upside-down grubs are surprisingly fast.
Despite their large size, green June beetle larvae seldom cause injury to turf equal to that caused by Japanese beetles or masked chafers. They are mostly considered a nuisance pest. Control efforts should focus on reducing organic matter, particularly thatch, beneath infested lawns. For example, thatch reduction using core aeration to enhance aerobic decomposition will eventually make infested lawns less attractive to these buzz-bombing beetles.