Participants in this week’s OGIA/OSU Extension Greater Cincinnati Diagnostic Walkabout were treated to large numbers of buzz-bombing Green June Beetles (Cotinis nitida, family Scarabaeidae) cruising turfgrass. Although adults usually emerge in Ohio in early July, the native beetle has a wide geographical distribution in the U.S., with adults appearing in June in its southern range, which accounts for the common name.
Adults have a matte finish, and as shown in the image below, there are different color forms. Some are solid emerald-green, while others sport variations of a brown on green color motif.
The big beetles typically gather en masse to terrorize gardeners, golfers, sunbathers, small children, and pets as they buzz over home lawns and golf courses. They are day-fliers and make an audible "buzzing" sound as they follow a low-level flight plan, cruising at about 2 – 3' above the ground, punctuated by occasional dips and erratic turns. They commonly orbit distinct patches of grass, behaving almost as if their flight patterns are confined by an invisible beetle fence.
Of course, birds don’t ignore such a large gathering of potential meat items. A study published in 2016 showed that green June beetles commonly drew the attention of blue jays (Cyanocitta cristata) and common grackles (Quiscalus quiscala) with the jays appearing to selectively feast upon female beetles.
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. The same is true with golf courses, with the beetles focusing on certain areas.
Unlike many of their scarab cousins, green June beetles do not feed on plant leaves. The adults have blunt spatulate mandibles adapted to a “soft diet.” They feed on plant juices, oozing sap, and can forage on overripe fruit, which accounts for the beetle’s alternate common name of “fig eater.” They will also feed on fruit that’s been damaged by other insects, such as Japanese beetles (Popillia japonica).
Since the adults don’t have typical chewing mouthparts, they can’t bite. However, based on firsthand experience, they can deliver painful skin pricks using their sharp spurs located on their legs. During the walkabout, I tried holding beetles in my closed hand until I could take pictures, but it was like holding thorny rose stems. I had to let them go after mumbling a few expletives.
On a side note, I don’t remember being “spurred” by green June beetles as a boy growing up in West Virginia. With limited entertainment options, we were often left to our own devices. Some amusements were even safe. One diversion involved tying a string around the hind leg of a green June beetle. When released, the tethered beetle would resume flying but remain anchored to our hand. Our parents loved the activity because it rarely ended with a trip to a hospital emergency room. But there’s that time I elevated the entertainment value by standing on a barn roof.
NOTE: No beetles or entomologists were injured during the making of this demonstration.
Robert Pemberton published a paper in Florida Entomologist in 2010 in which he describes growing up in Kentucky and “flying” green June beetles for entertainment. Later in life, while working in West Africa, he observed a small boy “flying” a scarab beetle at the end of a thread. He also noted that scarabs were flown by children in other parts of Africa. He speculated that the pastime may have been introduced from Africa into the American South by enslaved people.
The Grubs Do the Backstroke
Green June beetle grubs are one of the largest and strangest white grubs in Ohio. The mature grubs look like white grubs on steroids, measuring well over 1" in length.
The huge grubs also practice an unusual mode of locomotion. They crawl on their backs in an undulating, rolling motion that causes them to superficially resemble caterpillars. Their legs are smaller than those of other white grubs, particularly in comparison to the size of their bodies. Some have speculated that their leg size is an adaptation to life in a burrow, while their unusual style of crawling reconciles having big bodies and small legs.
I posted a YouTube video showing this unusual upside-down crawling. You can view the video by clicking this hotlink:
https://youtu.be/EF8UeznxE5M
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. Much of their damage to turfgrass is associated with their burrowing and tunneling behavior, given that they primarily feed on decaying organic matter. However, they have been known to feed on turfgrass, producing damage that appears as irregular patches.
The grubs venture out of their burrows in the late evening or during the night to feed or to go on an upside-down crawl-about in search of more food. They may also be driven out by heavy rains to appear in large numbers, meandering across driveways and sidewalks or dropping into swimming pools.
Management
Despite their large size, green June beetle grubs seldom cause injury to turf equal to that caused by Japanese beetles or masked chafers (Cyclocephala spp.). They are generally 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 may eventually make infested lawns less attractive as grub development sites to these buzz-bombing beetles.
Applications of organic matter to turfgrass should also be used with caution. Anecdotal reports from turfgrass managers and others have pointed to a link between extremely heavy applications of garden compost or composted sewage sludge and the subsequent appearance of the buzz-bombing beetles the following year. Indeed, a study published in 2001 showed a correlation between beetle egg-laying and the application of organic fertilizers.
A Twofer: Green June Beetle Nemesis and Plant Pollinator
The Blue-Winged Wasp (Scolia dubia, family Scoliidae) is named for its dark blue wings. However, one of its more striking features is two prominent yellow spots on a black background on the third abdominal segment.
This large hairy wasp is a plant pollinator and may be spotted in late summer to early fall scrambling around on flowers to sip nectar. I’ve observed them on a wide range of late-season flowers, but I most often find them on common goldenrod (Solidago canadensis).
Scoliid wasps are parasitoids of scarab beetles, and blue-winged wasps continue the family tradition: they are the nemesis of green June beetles. Females dig into the soil until they find a green June beetle grub, or they will simply enter the grub's soil burrow.
The wasp stings and paralyzes the grub, then they lay an egg on the grub's body. When the egg hatches, the wasp larva feeds leech-like on its hapless grub victim until the grub is no more.
Later this season, you may see blue-winged wasps making low-level flights only a few inches above turfgrass infested with green June beetle grubs. It’s important to remember that, just like in American Graffiti, the cruisers are males. So, they can’t sting. They are awaiting the emergence of females to … get acquainted. Although the females can sting, they are not aggressive. I’ve gotten very close while taking pictures and have never been buzzed or otherwise threatened.
The bottom line is that blue-winged wasps provide a twofer, both as a pollinator and a parasitoid. It proves the value of providing a nectar source, in this case, goldenrod, to help draw in an enemy of an insect pest. It's a good example of how butterfly gardens (a.k.a. pollinator gardens) can serve as an important component in an overall pest management strategy.
Selected References
Alcock, J. (2016). The Scramble Competition Mating System of Scolia dubia (Hymenoptera: Scoliidae). Journal of the Kansas Entomological Society, 89(2), 168–173.
http://www.jstor.org/stable/44594835
Alcock, J. (2016). The green June beetle (Cotinis nitida)(Coleoptera: Scarabaeidae): local variation in the beetle’s major avian predators and in the competition for mates. Journal of Natural History, 50(11-12), 661-667.
https://doi.org/10.1080/00222933.2015.1082657
Brandhorst-Hubbard, J. L., Flanders, K. L., & Appel, A. G. (2001). Oviposition site and food preference of the green June beetle (Coleoptera: Scarabaeidae). Journal of Economic Entomology, 94(3), 628-633.
https://doi.org/10.1603/0022-0493-94.3.628
Hammons, D. L., Kurtural, S. K., Newman, M. C., & Potter, D. A. (2009). Invasive Japanese beetles facilitate aggregation and injury by a native scarab pest of ripening fruits. Proceedings of the National Academy of Sciences, 106(10), 3686-3691.
https://www.pnas.org/doi/abs/10.1073/pnas.0811097106
Pemberton, R. W. (2010). The flying scarab beetle games of West Africa and the American South: Cultural transfer or parallel evolution?. Florida Entomologist, 93(4), 647-648.
https://doi.org/10.1653/024.093.0427
