On a hot summer’s morning last week, while sitting on a stoop, I noticed large bumble bee–like creatures zooming 14 inches above the surface of a lawn. When the sun hid behind a cloud for a few moments, the zoomers disappeared, and within moments of the return of bright sunshine, the aerial acrobats returned. Occasionally one of the fliers would dive-bomb into the turf. After examining one such crash site, I realized these were not demented bumble bees, rather they were very large scarab beetles known as Green June beetles. The flight patterns and buzzing sounds of Green June beetle adults are strongly reminiscent of large bumble bees. Perhaps, these behaviors are a clever way to ward off would-be predators that have learned not to mess with large, buzzing, stinging insects.
After two years of ample spring and early summer rainfall, members of the scarab clan are having a heyday. Last year we visited Japanese beetles and Asiatic garden beetles as they ravaged lawns and shrubs. A few weeks ago we visited Oriental beetles as they devoured flowers in my garden. Now is the time to enjoy another member of the scarab clan that also seems to be thriving in these uber-moist conditions.
Green June beetles are part of the scarab beetle clan known as fruit and flower chafers, or Cetoniinae. While most beetles spread their hard outer wings to fly, Green June beetle and their kin simply lift their hardened outer wings, expand membranous hind wings, and take off. Male beetles zoom in the morning as they search for mates. Females also fly low as they search for suitable places to deposit eggs in the soil. Once the female locates a favorable spot, she burrows several inches into the earth, makes a large sticky ball of soil and proteinaceous goop (technical term), and deposits eggs in it. Eggs hatch in a few days into small c-shaped white grubs. During the day the white grubs rest in a burrow underground, but at night they move to the surface of the earth to eat decaying organic matter.
With some regularity, in late summer and autumn these rather large white grubs wind up on my patio or in the carport. These unusually large grubs have an unconventional mode of getting from place to place. Although Green June beetle grubs have well developed legs on their thorax, legs are not the primary mode of locomotion when they rise from the earth. These wiggly critters have a series of stout hairs on the upper surface of their back. To move above ground, the grub rolls onto its back and with peristaltic motions it wriggles across the surface of the ground. The stout dorsal hairs contact the substrate and provide ample traction for surprisingly rapid movement.
Soils with organic mulches and farm fields that receive applications of manure are highly attractive to the egg-laying females and may be loaded with grubs. Most of the damage caused by grubs results as they move to the surface of the soil to feed. Their burrows can be the diameter of your thumb and small mounds of soil often surround the burrows. The disruption of soil caused by burrowing beetles creates problems on golf courses and in lawns. After feeding for several months near the surface of the earth, the grubs, which may be an inch and a half long, burrow deeper underground to escape winter's bitter cold.
In spring as temperatures warm, larvae return to the upper stratum of the soil to resume feeding and complete development. Unlike their more destructive relatives, Japanese beetles, Asiatic garden beetles, and Oriental beetles, Green June beetles are not serious pests of roses, lindens, or other plants. Their primary foods are thin-skinned fruits such as berries and grapes. I have also observed several adults congregating on a wounded tree to slurp fermenting exudates. Fresh fruit and fermenting beverages sound just fine on a warm summer’s day. Maybe these Green June beetles are just a bit smarter than we think.
Green June beetles love fruit. Share a slice of pear with one now and then.
Much of the information for this Bug of the Week came from Daniel Potter’s excellent reference book “Destructive Turfgrass Pests”, Ann Arbor Press, and the interesting article “Mimicry of Hymenoptera by Beetles with Unconventional Flight” by R.E. Silberglied and T. Eisner.
To learn more about Green June beetles online, you can visit the following web site: