Japanese Beetle

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Japanese Beetle

The scarab beetle is widely known across the planet for its variety and colors. The Japanese beetle is one of the most famous beetle species from the scarab group. The body measurements of an adult Japanese beetle are usually 15 mm in length and 10 mm in width. Because of this, the body of the beetle looks different than other beetle species. However, in the case of Japanese beetles, the elytra are remarkably different than others with the same matte copper color. The thorax and the head of this species are green-colored, ideal for camouflaging while the beetles look for meals.

On each side of the body, there is a row of noticeable white spots present. The spots are mostly present in the lower portion of the wings. The color-contrast and variety of body patterns make the beetle look mysterious and enchanting. A special trait of Japanese beetles is that they eat greens in an almost artistic way: the pattern this insect creates on a leaf makes a tree look like its skeletal remains.

Japanese beetles consume the green parts of the leaf, leaving the veins. This makes their eating pattern appear creative and organized. The adult beetles of this species may also feed on fruits and flowers of the plants, while the younger, immature beetles (the larvae) feed on the roots of grass.

Availability, Distribution, and Habitat

Japanese Beetle

The adults usually start flying in June and they are found most active in the months of July and August. The adult beetles usually expire after August. The usual life expectancy of the Japanese beetle is 30 to 45 days.

Though the species is named after Japan, the presence of Japanese beetles is mostly detected in the United States. The first evidence of Japanese beetles was found in the United States in the year of 1916. The place was located in New Jersey. Later the reach of the Japanese beetle extended up to the Mississippi River (excluding Florida). They are also found in some parts of Minnesota, Missouri, Kansas, and Oklahoma. Lately, as the studies show, evidence of Japanese beetles has been recorded in Texas, Washington, and particular regions of North Dakota.

When it comes to habitats, Japanese beetles always exist alongside others, and the species also prefers changing places by taking their entire group along. They are mostly active on sunny days in a hot climate. This is mainly due to their preference towards feeding on plants that are placed under direct sun. Male beetles are much more mobile than females. They can move fast from one area to another miles away, in search of a greater region of greens.

Life Cycle

Researchers have observed that it takes almost a year for a Japanese beetle to complete its life cycle. In colder climates, it may take one and a half years, and a maximum of two. Some important factors that can control the life cycle timing and pattern of this beetle are the yearly variance in latitude and longitude. The population of this species is well controlled by keeping the sex ratio 1:1. The fully grown adults leave the ground after the final stage, looking for a mate and engaging in reproductive activity. Female beetles are more aware and sensitive than male beetles in the case of reproduction.

The female Japanese beetles usually leave the tree branches by the afternoon to find proper soil to burrow and lay eggs in. A female beetle can produce a total of 40 to 60 eggs in her lifetime. The eggs are placed in the soil. After feeding on roots and other organic matter, the larvae turn into grubs in a short period of time. The white grubs keep themselves hidden in the soil to avoid predators. The grubs can survive in any soil that can sustain trees. They feed on soft tree roots and sometimes vegetable seedlings.

A special thing about Japanese beetle grubs is that they can withstand the soil-moisture. Heavy summer rainfall does not affect them in any way. In fact, the rainfall is sometimes necessary to prevent the grubs from getting dry and dying. By chewing grass-roots, the grub’s shell becomes a source of water with which they can survive hot weather and the sun. The grubs move deeper into the soil for safety, particularly during winter when the temperature of the soil increases.

Most of the grubs spend the winter 2 to 6 inches under the surface of the soil as their body becomes inactive. When finally the temperature of the soil rises above 50 degrees, the grubs start to climb towards the surface. Within a period of 4 to 6 weeks during the final stage, adults break out of the pupal body and come to the surface fully developed.


The damage done by Japanese beetles is nearly impossible to recover. Since the beetle chews the green parts of the leaves edging the veins, the structure of the plants literally collapses. The beetles chew the plant from the top down, meaning the entire process flows vertically from the top to the bottom of the tree.

Additionally, as the grubs feed on grassroots, the roots become weak. The capacity of the grasses to preserve water fails, and that eventually makes the grasses unable to withstand hot weather and direct sun. Once the Japanese beetles attack the plants in groups, it becomes almost impossible to save the trees from dying.


There are two primary ways in which Japanese beetles can be controlled: physical removal from trees, and cultural control. Since the beetles are less active in cold weather, it is easy to pick and remove the beetles from the trees in the early mornings of winter. Also, the female beetles look for the moist soil required for laying eggs. So, holding back irrigation in the peak beetle activity hours may reduce the population of the grubs in the soil, which will eventually result in a smaller population of the species.

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