What Is a Japanese Beetle?
The Japanese beetle (Popillia japonica) is a type of scarab beetle native to northern Japan. It came to the U.S. in the early 1900s, likely through the soil that came with imported plants. Since then, the Japanese beetle has spread throughout much of the Eastern and Central U.S., reaching just past the Mississippi River.
Are Japanese beetles invasive?
Yes. In the U.S., they're an invasive pest that can damage crops, landscape plants, and lawns. They're very difficult and costly to control.
What does the Japanese beetle look like?
Japanese beetles have shiny, metallic green bodies and six legs. Adults are about 1/2 inch long. The tips of their antennae (feelers) can open like a fan. Along each side of their bodies, under the wing shields, Japanese beetles have tiny patches of white hair that look like spots or stripes from a distance. This helps distinguish them from other beetles.
Young Japanese beetles are called larvae or grubs. Their bodies are about an inch long and curled into a C shape. Japanese beetle larvae have brown heads, white bodies, and six legs.
What does the Japanese beetle eat?
When the larvae hatch from their eggs, they eat the roots of plants, especially grasses. They feed in the top 2-4 inches of soil until they're almost full-grown. Toward the end of fall, the larvae burrow down about 4-8 inches, where they hibernate during the winter. In early spring, they come back up to eat roots again. In May, the larvae enter the pupa stage, when they form a protective covering around themselves while they change into an adult beetle.
Adult Japanese beetles come out in June or July and live for about two months. They fly around and feed during the day and are especially active when it's hot and sunny. They eat the leaves, flowers, and fruits of more than 300 types of plants. In the vegetable garden, Japanese beetles especially like corn, beans, basil, and tomatoes.
Where Do Japanese Beetles Live?
In its native country of Japan, the Japanese beetle is not a major pest. The native plants in Japan have likely developed resistance to the beetle. Native animals that eat Japanese beetles keep their numbers down, and climate and insect diseases may also play a part. In the U.S., the Japanese beetle has few natural enemies or diseases and can spread quickly.
People first identified a Japanese beetle in the U.S. in 1916 in a plant nursery in New Jersey. The Japanese beetle has now spread to more than 35 states. All of the states where there's an established population of Japanese beetles (where they consistently live and mate) are located east of the Rocky Mountains. The U.S. Department of Agriculture works with university extension and state agriculture departments to keep the Japanese beetle from spreading to Western states.
Signs You Have Japanese Beetles
Adult Japanese beetles eat the soft parts of leaves between the veins. They often leave only a lacy skeleton, but you may also find large, uneven holes in leaves. Trees that lose a lot of leaves to Japanese beetles may turn brown and start to drop leaves. Japanese beetle grubs create patches of pale, dead, or dying grass. These patches can spread and join together until the turf can be rolled up like a carpet because there are no longer enough roots to attach it to the ground.
In your yard, you would see adult Japanese beetles on the tops of plants during the day, especially when it's sunny and warm. They tend to eat together, so you may find up to 25 beetles on one plant. You can find Japanese beetle larvae feeding on grass roots under patches of dead grass.
Why Do You Get Japanese Beetles?
Japanese beetles can fly several miles to find food and may find your yard attractive if it offers them any food sources. Adult beetles also need a place to mate, which is usually on or near the plants they eat. They lay eggs in the same area, but they'll search for a well-watered grassy spot. Even in dry parts of the country, lawn sprinklers provide enough moisture for the eggs to develop into larvae.
Plants most affected by Japanese beetles
Among landscape plants, Japanese beetles have definite favorites, including:
How to Prevent an Infestation
There is no simple way to prevent Japanese beetles. It takes a multipronged attack, but if you start controlling the growth cycle early, you may avoid the damage they bring later.
Start at the grub stage. Grubs are known for being difficult to get rid of. But there are different methods you can try, including natural and chemical treatments. Consult your local extension to find out which is best for your area because different methods work better in certain climates.
Plant beetle-repellent and resistant landscape plants. Companion planting with plants such as catnip, marigold, garlic, and chives can help repel Japanese beetles. And plant those among beetle-resistant plants, such as begonias, impatiens, and lantanas.
Add native insects. Try attracting native wasps and flies to your garden. They're predators of beetles, but they likely just attack larvae.
Are Japanese Beetles Dangerous?
Not unless you're a landscape plant. Japanese beetles don't bite or sting people, so they're not dangerous to humans. But they are considered very harmful to plants.
How to Get Rid of Japanese Beetles
Adult beetles stay on the tops of host plants, and the larvae live underground, so you must use a combination of the methods outlined below. To see results, you must work on reducing the number of both adult beetles and larvae.
Careful planting. When choosing new plants, avoid planting favorites of the Japanese beetle. Instead, pick plants that are more resistant and tend to repel them, including:
- Flowering dogwood
- Red and silver maples
- Magnolia
- Common lilac
- Holly
- Begonia
- Tulip tree
- Hosta
- Boxwood
- Lantana
Physical removal. On cool mornings, when beetles are less active, handpick them off small plants and toss them into a bucket of soapy water. For shrubs and trees, shake the plant or its branches over your bucket of soapy water.
Barriers. Protect particularly valuable vegetables, shrubs, and small trees by covering them from late June through early September. Use cheesecloth, nylon insect screens, or other netting with a mesh size of no more than 1/4 inch. Attach the edges of the netting to the ground.
Weeding. Get rid of any weeds on your property that Japanese beetles like, such as:
- Poison ivy
- Bracken
- Smartweed
- Elder
- Wild grape
- Indian mallow
- Multiflora rose (an invasive species)
Lawn care. A dense, healthy lawn draws other insects that can keep grubs under control. Using fertilizers properly, watering when there's little rain, and mowing at a 3-4 inch height can help.
Chemicals. If you decide to use an insecticide (a chemical designed to kill insects), check the label to make sure it says that it works on Japanese beetles and that you can use it to treat the types of plants you plan to spray. Read the directions carefully and follow them to the letter. Be especially careful if you're growing food. Read the label for instructions about how long you must wait to harvest after spraying.
Biological control. There are specific types of parasites that target Japanese beetles. These include certain species of wasps, nematodes (microscopic roundworms), and bacteria. Check with your local extension agent to find out what biological controls are available in your area. Some of these can be sprayed on your plants or lawn like a chemical insecticide. If there's an established population of parasitic insects in your area, you may be able to plant trees or flowers that will attract them to your yard.
Bag traps or other beetle traps use pheromones to lure and capture them. But these traps attract a lot of Japanese beetles, and not all get captured, so they can end up doing more harm than good.
Japanese Beetle FAQs
What is the natural enemy of the Japanese beetle?
One of the most common natural enemies of the Japanese beetle is the tachinid fly. Other natural enemies include spiders, assassin bugs, predatory stink bugs, and birds. But none of these have been truly effective in controlling Japanese beetles.
What smell do Japanese beetles hate?
Japanese beetles may be repelled by the strong scents of plants such as catnip, marigolds, garlic, and chives.
What is the best killer for Japanese beetles?
There is no one best killer of Japanese beetles. They are notoriously difficult to get rid of. It takes a multipronged approach of preventive and control measures to rid your garden of these invasive pests.