Japanese beetles are eaten by a surprisingly wide range of predators, parasites, and microscopic organisms that attack both the adult beetle and its soil-dwelling grub stage. Birds, skunks, raccoons, parasitic wasps, tachinid flies, and beneficial nematodes all feed on Japanese beetles at various points in their life cycle. Understanding what eats them can help you encourage these natural enemies in your yard.
Birds That Eat Japanese Beetles
Many common backyard birds feed on adult Japanese beetles, including starlings, grackles, cardinals, catbirds, robins, and crows. Robins are particularly effective because they hunt both the adult beetles on plants and the grubs in soil. You can often spot robins pulling grubs from lawns in spring and fall when the larvae are closest to the surface. Maintaining bird-friendly habitat with native trees, shrubs, and a water source helps keep these predators around during peak beetle season in summer.
Skunks, Raccoons, and Moles
Skunks and raccoons are voracious grub predators. They can smell Japanese beetle larvae beneath the turf and will dig them out at night, sometimes so aggressively that a lawn looks like it has been rototilled. If you wake up to patches of sod peeled back or small cone-shaped holes across your yard, skunks or raccoons feeding on grubs are the likely cause. The lawn damage these animals inflict can actually be worse than the grub damage itself.
Moles also feed heavily on Japanese beetle grubs as they tunnel through soil. Mole activity in your lawn is often a sign that grub populations are high underground. While moles are insectivores rather than rodents, their tunneling disrupts root systems and creates visible ridges across the lawn surface.
Parasitic Wasps That Target Grubs
Tiphia wasps are among the most effective natural enemies of Japanese beetle grubs. These small, non-aggressive wasps burrow into the soil, locate a grub, sting it to temporarily paralyze it, and lay a single egg on its body. The wasp larva hatches and feeds on the grub, eventually killing it. There are two species active at different times of year: one in spring and one in summer.
You can attract Tiphia wasps to your property by planting specific flowers that provide them with nectar. Spring Tiphia wasps are drawn to peonies, which secrete nectar through the base of unopened flower buds. Cultivars like ‘Big Ben,’ ‘Bowl of Beauty,’ ‘Festiva Maxima,’ and ‘Sarah Bernhardt’ have all been shown to attract these wasps. Conveniently, peonies are not damaged by adult Japanese beetles. Summer Tiphia wasps feed on nectar from wild carrot (Queen Anne’s lace), so leaving some of these plants in your landscape gives them a food source during the later season.
The Winsome Fly
The winsome fly is a parasitic fly introduced to North America specifically to control Japanese beetles. Female flies land on adult beetles and lay an egg just behind the head. Within a few days, the larva hatches and uses serrated mouthparts to bore through the beetle’s outer shell and begin feeding internally. The parasitized beetle stops eating within three to four days and dies within five to ten days. The fly larva then pupates inside the beetle carcass and overwinters there until the following summer.
Winsome flies prefer to lay eggs on female Japanese beetles, which has a compounding effect on population control since each parasitized female produces no offspring. When beetle populations are low, multiple fly eggs may end up on a single beetle. These flies have become established across much of the upper Midwest and Northeast and require no action on your part to benefit from their presence.
Beneficial Nematodes
Microscopic roundworms called beneficial nematodes are one of the most practical biological controls you can apply yourself. The species Heterorhabditis bacteriophora is the most effective against Japanese beetle grubs and outperforms other commonly sold nematode species. These nematodes enter the grub’s body, release bacteria that kill the larva within a day or two, and then reproduce inside the carcass. The next generation of nematodes disperses into the surrounding soil to find new hosts.
You apply beneficial nematodes by mixing them with water and spraying or watering them into your lawn, typically in late summer or early fall when grubs are small and near the soil surface. The soil needs to stay moist for several days after application so the nematodes can move through it. They’re sold refrigerated and have a limited shelf life, so timing your purchase with your application matters.
Milky Spore Disease
Milky spore is a naturally occurring soil bacterium that infects and kills Japanese beetle grubs. When a grub ingests the spores, they germinate in its gut within two days. The bacteria multiply, penetrate the gut wall, and spread through the larva’s body over the next one to three weeks until the grub takes on a characteristic milky white appearance and dies, releasing billions of new spores into the soil.
A large-scale U.S. government program between 1939 and 1953 applied over 100 tons of milky spore powder across more than 160,000 sites. Grub populations in treated areas dropped 10- to 20-fold and stayed at those lower levels. However, more recent evidence from Cornell University suggests the bacterium may be losing effectiveness in some regions. Field surveys have found that only about 0.2% of collected grubs showed signs of milky spore infection, compared to 41.5% in 1946. A separate field study in Kentucky found that commercial milky spore products were only moderately effective, infecting 39 to 44% of grubs, and that infected grubs still consumed the same amount of roots as healthy ones before dying. If you’re considering milky spore, it works best in warmer climates where soil temperatures support bacterial activity, and it can take two to three years to fully establish in your lawn.
Other Insect Predators
Ground beetles, ants, and predatory stink bugs all feed on Japanese beetle grubs or adults opportunistically. Assassin bugs will prey on adult beetles when they encounter them on foliage. Spiders, particularly orb weavers, catch adult beetles in their webs during summer flights. None of these predators specialize in Japanese beetles the way Tiphia wasps or winsome flies do, but together they contribute to overall mortality, especially in yards with diverse insect communities and minimal pesticide use.
Reducing broad-spectrum insecticide applications is one of the simplest ways to protect the full range of Japanese beetle predators. Many of the organisms that eat Japanese beetles, from parasitic wasps to ground beetles to nematodes, are killed by the same chemicals used to target the beetles themselves. A yard that supports predator populations year-round will generally have fewer Japanese beetle problems over time than one relying solely on chemical treatments.