Japanese Beetle

My assigned bug is the Japanese Beetle, known to scientists as Popillia Japonica.

A common Japanese Beetle
A common Japanese Beetle

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Scarabaeidae
Genus: Popillia
Species: Popillia Japonica


A detailed key to the morphology of the Japanese Beetle
A detailed key to the morphology of the Japanese Beetle

The Japanese Beetle Grubs (or larvae) are very typical, simple grubs. However, they are unique because of the fact that they have a V-shaped series of bristles on their raster. The youngest grubs can be 1.5 mm long, but the most mature can be up to 32 mm.

The youngest pupa are cream colored and gain a reddish hue as they age. They are roughly 14 mm long and 7 mm wide. The insect commonly stays in this stage for about two weeks to a month.

A Japanese Beetle egg is about 1.5 mm long and 1 mm wide. Being so, they are not very round. When they are deposited in the ground, they absorb the surrounding moisture and become more round. They are very white. The eggs are typically laid in small groups, usually 6.

Japanese Beetles are about 15 mm long and 10 mm wide. They have a metallic green head, thorax and pronutum, along with a copper elytra. They have several tufts of white hair along the sides of their elytra, exactly 5 on each side, and 2 on the very rear. They have a dark green scutella which continues as a line until the rear of the elytra is reached. Japanese Beetle antennae are about 7 segments and flatten, at the ends, to form 3 flat planes known professionally as lamellae.

Distinguishing Characteristics-
The Japanese Beetle looks very noticeable because of their striking beauty. However, the grubs look very typical. They can be distinguished by the arrangement of their hairs on their raster. This arrangement is elaborated upon in the "raster" link and is provided along with a helpful diagram. The adults are typically distinguished by their 5 tufts of white hair along the sides of their elytra and the two tufts on their rear.


The Japanese Beetle is typically found in open meadows, fields, gardens, or woods. It always lives in wide, lush areas, typically in the east of North America. However, they are very flexible with their habitat because of their amazingly wide variety of consumable plants. This way, it can also infest citizens' lawns and even some urban landscapes. The grubs can feed on the roots of grass, so a japanese beetle can (in theory) thrive in any area with grass. They are extremely flexible in terms of their habitat, as they have moved across all of at least 22 states and even into Canada.

Geographic Range

The Japanese Beetle originated in Japan (obviously). However, it has now spread to the United States and exists in 22 states east of the Mississippi and some of Ontario, Canada. The species was introduced in the early 20th century, in 1916 to be exact, by way of hiding in Iris roots. The species thrives in Canada and northern areas, as it is at its prime in cold weather. It is so comfortable in Japan because most fields are at a high altitude and thus are colder. These beetles naturally bury their eggs in the dirt under the grass found there, which acts as a food source for the grubs. So, it is quite reasonable how the Japanese Beetle lives twice as long in its native Japan than in the United States and Canada. However, quite ironically, Japanese Beetles are not that devastating in Japan, as their population is put in check by their natural predators. However, in the United States, they are able to grow to their full potential, as they are not limited by as many predators as in Japan. There is a video to the right which stresses how powerful japanese beetles can be without their natural predators, and how humans are trying to put them in check.

Mating Behavior

Japanese Beetles exercise a common behavior in the insect world; Mate Guarding. This term belongs to the instances where male insects stay close to their future mates, so their mate is not stolen by another insect. This is usually accomplished by the male laying on top of the female until the female is ready to mate. When it is, the beetles reproduce sexually, much like humans do. These insects still go through the processes of meiosis and fertilization, only with a smaller number of chromosomes than humans (20 versus 46). Female Beetles of this species appear just like males, so there does exist some confusion when mating. Females are generally slightly larger than males, so males will typically stop guarding their current mate if they find a larger one to be around.

external image JapaneseBeetle.gif

Life Cycle

Japanese Beetles always begin life as an egg. The eggs are typically laid about July or August, in groups of five or six, until about 60 eggs have laid in all. The insect stays as an egg, absorbing moisture, until about the middle of August or September. At this point, the egg hatches to reveal a typical white grub which remains a grub until June. In June, the grub cocoons itself and stays that way for roughly a month. When the cocoon hatches, a typical Adult Japanese Beetle is revealed, which finally leaves the ground and feeds on the surrounding plants until the end of July or beginning of August, where it mates, lays its eggs, and soon dies. The diagram to the right helps to illustrate this. During the excluded months, the larvae overwinter and develop.

Feeding Habits

The dramatic effects of a group of Japanese Beetles are shown here.
The dramatic effects of a group of Japanese Beetles are shown here.

The Japanese Beetle can feed on what some estimate to be over 400 different plants, but others estimate around 200. The adults feed upon beans, strawberries, tomatoes, peppers, grapes, hops, roses, cherries, pears, rasperries, corn and even more. They also eat the leaves of birch trees and basil. These bugs can be highly mobile and, being so, can fly many miles to feed or lay new eggs. Japanese Beetles typically eat plants from the top to the bottom. They can even eat some flowers and petals, such as roses. Grubs, in their first stages of life, eat only decomposing matter. However, they soon grow to consume more challenging foods, such as various roots.

Ecological Role

Japanese Beetles are generally seen as a nuisance to gardeners, farmers, or anybody else who wants their foliage to look nice. Solitarily, a single Japanese Beetle does not do much harm to a plant. However, when several of them work together, they can outright destroy plants. Adults devour the soft tissue between the leaves of the trees and leave the tree with a skeletonized, scorched appearance. Grubs consume the roots of the grass underneath the ground. These two combinations together can leave horrible effects on one's foliage. There are several videos and podcasts on how to stop these insects, a podcast is shown as an example below. It shows a surplus of information on how Japanese Beetles affect one's lawn, and what foliage to plant in order to drive away the beetles.













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