Adult June bugs eat leaves, tree sap, and ripe fruit, while their larvae (white grubs) feed on plant roots and decaying organic matter in the soil. What a June bug eats depends entirely on its life stage, and the grub stage actually causes far more damage than the flying adults most people notice buzzing around porch lights.
What Adult June Bugs Eat
Adult June beetles emerge in late spring and summer to feed and mate. They’re nocturnal feeders, most active just before and after sunset. The common brown May/June beetles (Phyllophaga species) prefer the foliage of broadleaf plants, conifers, and oak trees. They chew on leaves under cover of darkness, and when populations are high, they can strip young trees bare. In avocado groves, for example, adult beetles flying in from nearby brush land have been documented defoliating large numbers of young trees night after night.
Green June beetles (the iridescent green ones) have different tastes. They go after ripening and overripe fruit, including peaches, grapes, raspberries, blackberries, apples, pears, plums, apricots, and nectarines. They also feed on tree sap from oaks, maples, and other species, and on ears of corn still growing in the field. Green June beetles use a small horn on the front of their head to gouge into undamaged fruit, then feed on the flesh inside. Several beetles will sometimes bury themselves entirely in a single ripe peach.
What June Bug Larvae Eat
The larval stage is where June bugs do their real eating. June bug larvae are white grubs: plump, C-shaped, cream-colored creatures that live underground for one to three years depending on the species. When they first hatch, they feed on decaying organic matter in the soil. As they grow, they shift to feeding on living plant roots using strong chewing mouthparts that shear through root hairs and lateral roots.
The menu is broad. Grubs feed on the root systems of turfgrass, corn, soybeans, potatoes, cereals, vegetable crops, nursery stock, pasture grasses, and the roots of trees and shrubs. Second-year larvae cause the most damage because they’re larger and eating more aggressively. Green June beetle larvae specifically prefer decaying organic matter and are often found in well-rotted manure or compost piles rather than living roots.
How Grub Feeding Damages Lawns
If you’re finding June bugs around your home, the real concern is usually what their offspring are doing to your lawn. Grubs sever grass roots below the surface, and heavily damaged turf pulls up like a loose carpet. Healthy, well-watered turfgrass can tolerate a surprising number of grubs. Most lawns handle 6 to 8 grubs per square foot without visible problems. Well-managed turf may tolerate up to 20 per square foot. Stressed lawns, though, start showing symptoms at 8 or more per square foot, and populations above 7 per square foot can result in complete root loss.
Even before grub damage becomes visible in the grass itself, you might notice a secondary problem. Skunks, raccoons, armadillos, and birds dig up turf to get at the grubs, tearing apart lawns that might otherwise have survived the root feeding. This animal damage often shows up before the grass itself dies back, which is why some experts recommend treating at a lower threshold of 4 to 5 grubs per square foot.
Why Life Stage Matters More Than Species
June bug is a loose common name that covers dozens of scarab beetle species. The brown Phyllophaga beetles, the metallic green Cotinis beetles, and various smaller species like Serica all get lumped together. Their diets vary somewhat by species, but the bigger distinction is always between the adult and larval stages. Adults are above-ground feeders that target leaves, fruit, and sap for a relatively short period during their mating season. Larvae are underground feeders that spend one to three years steadily consuming roots and organic matter before pupating and emerging as adults.
The adults you see crashing into your windows on summer nights are feeding on nearby foliage, but they’re also laying eggs in the soil. Each female deposits eggs that hatch into grubs the same summer. Those grubs start small, feeding mostly on organic debris, then grow through the fall and winter. By their second year underground, they’re large enough to do serious damage to root systems. This long underground phase is why grub problems can seem to appear out of nowhere, months or even a year after the adult beetles were visible.
Plants Most at Risk
For adult feeding damage, oak trees are a top target for brown June beetles. Green June beetles zero in on stone fruits (peaches, plums, apricots, nectarines) and soft fruits (grapes, raspberries, blackberries) as they ripen. Overripe or damaged fruit is especially attractive. Young, newly planted trees near uncultivated land are vulnerable to defoliation because adult beetles fly in from surrounding brush.
For grub damage below ground, turfgrass lawns and golf courses take the biggest hit simply because grass root systems are shallow and dense, exactly the zone where grubs feed. Agricultural crops like corn, soybeans, and potatoes are also common hosts. Perennial grasses in pastures and conservation plantings provide a stable food source that supports grub populations over multiple years, which is why lawns adjacent to open grassland tend to have worse grub problems.