Japanese beetles are one of the larger insects in the garden and feed directly on fibrous foliage similar to a grasshopper or snail, rather than the sap-sucking aphids and mites. Beautiful and unmistakable for their metallic green and iridescent bodies, Japanese beetles are one of the most problematic pests in the eastern United States, as they are known to feed on just about anything from rose, bean, grape, and nearly any ornamental flower and fruiting tree. Leaf damage from the Japanese beetle is just as recognizable as the insect itself, as host plants become “skeletonized” after having eaten away their leaves, leaving behind the skeleton of the vascular system. First introduced to the United States in New Jersey 1916, the Japanese beetle is still fairly new to the country as its widespread in the east and still yet to truly make its way west.
Facts About Japanese Beetles
- Japanese Beetle Distribution: Invasive to eastern and midwestern states, abundant throughout Japan
- Japanese Beetle Host Plants: More than 300+ known species of rose bushes, fruit trees, and flowers
- Japanese Beetle Damage: Aggressively chewed, gnawed leaves and vegetation similar to grasshoppers
- Japanese Beetle Lifespan: 30-45 days
- Japanese Beetle Eggs Laid per Lifetime: ~60
- Japanese Beetle Removal: Organic pyrethrin, milky spore, neem oil, dish soap solution
- Japanese Beetle Predators: Wild birds, chickens, spiders, rodents
- Most Common Japanese Beetle in North America: Common Japanese Beetle (Popillia japonica)
What Do Japanese Beetles Look Like?
The Japanese beetle is a type of scarab beetle and unmistakable when compared to smaller, more common pests in the garden. Japanese beetles are about ½” long and just about the same width, sharing the same general hardshell features as all other scarabs. Synonymous with their metallic sheen, the Japanese beetle is exclusively iridescent bronze and metallic green and can be easily differentiated from other scarabs and pests. The Japanese beetle has six legs, two antennae that extend forwards from the top of their heads, and a large pair of wings on their back that makeup the iridescent bronze color of their body.
Japanese Beetle Damage
The Japanese beetle is one of the most aggressive and invasive pests in the United States as it's been slowly eating its way across the country for the last hundred years. Gardeners on the west coast have likely never seen a Japanese beetle, but those on the east coast and parts of the midwest have probably had a plant or two quickly “skeletonized” by a ravenous infestation.
Japanese beetles feed directly on the leaves of a host plant by aggressively ingesting the softest tissue of the leaf while leaving behind a vascular skeleton of its midrib and veins. Unlike the damaging but solitary snails and earwigs, Japanese beetles are a swarming insect and have the feeding capacity of a swarm of locusts.
What Do Japanese Beetles Eat?
The Japanese beetle is an invasive insect first recorded in the United States in Riverton, New Jersey nursery in 1916. Within just 4 years later the Japanese beetle was considered invasive as it had become too widespread to contain throughout the eastern half of the country. They’re known to directly feed on the foliage of more than 300 different species of plants including just about any rose, grape, fruiting tree, fruiting crop, hollyhock, and ornamental flower. Japanese beetles are still found exclusively in the eastern United States with some scattered throughout the Midwest and periodically some reported as far west as Wyoming and Colorado.
Japanese Beetle Eggs
Japanese beetle eggs are difficult to spot because they’re kept safe underground until hatching a few weeks later into a grub (larvae) which continues living underground for about 9 months until the following spring. These grubs bury deeper into the soil during the winter and continue to feed above the soil in the spring until ready to emerge as an adult fit to reproduce.
Japanese beetles prefer to lay their eggs underground in routinely moist, neat grass spaces such as golf courses and irrigated lawns. The small larvae, or grubs, are easily recognizable above the soil come spring but, generally by then, it’s too late to treat.
How To Get Rid of Japanese Beetles
Although much larger than some of the more popular garden pests, the Japanese beetle can be treated very similarly to aphids and mealybugs. Because Japanese beetles are a little bigger to eradicate, it is recommended to begin with a two-step process by first spraying infested hosts with an organic pyrethrin. Follow up with an application of either neem oil or a homemade dish soap-based solution. To help prevent eggs and grubs, add milky spore powder to your lawn available at just about any nursery. Milky spore is specifically made to kill Japanese beetle grubs and only needs to be applied to the lawn no more than once a year.