Interesting Facts About Japanese Beetles

Egg Laying

• The adult Japanese beetles mate soon after their emergence from the ground. The female digs as deep as 4 inches down into the ground and starts the egg-laying process, which can last for many weeks. The female lays up to four eggs every three or four days, mates again and lays more eggs. Some female Japanese beetles are capable of laying as many as 60 eggs during their life. The eggs are about a 16th of an inch in length and take on a more rounded form as they absorb water from the soil.

Grub Form

• The Japanese beetle grub spends as much as 10 months below the ground, feeding on such things as the roots of plants. The grub will tunnel farther down to avoid drought conditions in the upper layer of soil and to escape the cold winter. The average distance a grub moves vertically in the soil is usually about 30 inches, although some have gone as far as 16 feet to find food, notes the University of Kentucky College of Agriculture website. The grubs enter a pupae phase in late spring and come from the ground as adults by summer.

Odors

• The Japanese beetle is quite dependent on different odors because it selects its food often by smell. The first adults that make their way out of the ground and onto plants quickly start to eat. These beetles produce an odor that attracts the newly emerging adults to the food source. In addition, the females release a hormonal scent that brings males to them for mating purposes.

Effects

• Direct sunlight is usually a prerequisite for a Japanese beetle, as they prefer to eat plants exposed to full sun. The beetle by itself can do little damage over a short time, but the insects will amass on a plant and chew it up from the top portion downward. The Japanese beetle steers clear of tough foliage and eats the thinner leaves. With the ability to fly as far as five miles, the Japanese beetle can affect a large geographical area.

Predators

• The natural predators of this beetle include numerous birds that will gladly eat them when they encounter one. Species, such as the bobwhite quail, crow, grackle, starling, catbird, kingbird, robin and sparrow, all consume Japanese beetles. The grubs are vulnerable to ravenous shrews and moles, as well as skunks, a mammal that tears apart lawns and causes even more damage than the beetle grub will as it searches for a meal. Insects like the praying mantis eat Japanese beetles, as will species introduced from Asia to control beetle numbers, like various parasitic wasps and flies.