About Japanese Beetles

Japanese beetle grub © David Cappaert, Michigan State University, Bugwood.org
Japanese beetle grub © David Cappaert, Michigan State University, Bugwood.org

The Japanese beetle (Popillia japonica) is an introduced insect first discovered in the United States in New Jersey in 1916. It was accidentally brought into this country on iris roots from Japan. It can be found in nearly every state east of the Mississippi. It has spread rapidly due to lack of natural enemies.

The grubs (the larval or immature stage of the beetle) are possibly the most common lawn pest in New England. In fact, Japanese beetle grubs make up about 90 percent of the white grubs that live in Massachusetts lawns.

Identification

The adult beetle is 1/4 to 1/2 inch in length and metallic blue or green with coppery colored underside and wing covers. Patches of white hair can be found on the abdomen and below the wings. Adults emerge from the ground in late June and early July from the pupa state.

Warm, sunny days draw beetles out in larger numbers. They live only four to six weeks and are most active from about 9 am to 3 pm. The females lay eggs 30 to 45 days later and continue to be active in July and August.

Their eggs are yellowish-white, elliptical or spherical in shape, and are laid about 3 inches into the soil in grassy areas, often in closely cut grass. The females lay 1 to 4 eggs at a time and about 60 eggs during the season. They hatch into grubs in about two weeks.

The grubs can be recognized by the distinctive C-shape they take when curled up. They are white or cream in color, have three pairs of legs, and a hard brown head. The grub stage is about 10 months long. They then go into a brief pupa or resting stage in late spring where they change into a beetle.

Situations & Solutions

The non-native Japanese beetle can wreak havoc on yards, plants, and shrubs. They are the most destructive insect to lawns. Find out when to take action and what your management options are.