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Life Cycle of the Japanese Beetle

As their name suggests, Japanese beetles are native to Japan. The insects found their way into the United States via New Jersey in 1916. Because the beetles have no natural predators in the United States, they have spread across the nation and are now common pests for both farmers and gardeners. Japanese beetles feed on over 300 different plant species, and are especially fond of roses, grape leaves, fruit trees and birch trees.

Eggs
- Female Japanese beetles mate in the summer and lay one to five eggs at a time. They continue to do this every two or three days through July and August until they have laid between 40 and 60 eggs.
Grubs
- Japanese beetle eggs hatch eight to 14 days after they are laid. The baby beetle, known as a grub, burrows up to eight inches deep into the soil after hatching.
Growing Up
- Grubs spend the entire winter buried in the ground while they grow into adults. They climb to the surface in May and June as adult Japanese beetles after spending the first 10 months of their lives underground.
Identification
- Adult Japanese beetles are oval shaped with metallic green bodies and copper-colored wings. They are about 3/8 of an inch long and 1/4 of an inch wide. Grubs, looking nothing like adult beetles, are white, worm-like creatures that curl into a letter "C" when disturbed.
Beetles and Plants
- Japanese beetles in all stages of life are bad for plants. Grubs eat the roots of plants, and adult beetles eat the leaves.

Insects & Science