Sunday, July 17, 2022

What is, and is NOT, a Japanese Beetle

It is that time of year again in North America when everything is a Japanese Beetle. No matter whether you are a trusted and reliable expert, other people will insist that Green June Beetles, Fig Beetles, Dogbane Leaf Beetles, and various other beetles, are in fact Japanese Beetles. Why is this the case? There is much misinformation online and in the media. Family, friends, coworkers, and others present themselves as experts and make incorrect identifications. Mobile phone "apps" can also be misleading, given the relative infancy of image recognition software and deep learning, which frequently compounds errors instead of correcting them. Here is everything you need to know about how to recognize the Japanese Beetle, Popillia japonica, as well as lookalike species.

L-R: Japanese Beetle, Green June Beetle, Emerald Flower Scarab

The Japanese Beetle, as its name implies, occurs naturally in Japan and northern China. An accidental introduction of this species to New Jersey in 1916 is apparently what launched the beetle's domination of yards and gardens over most of the eastern United States and southeast Canada. It delivers a double whammy to urban and suburban areas by feeding on the roots of turf grasses in its subterranean larval (grub) stage, and on the foliage of more than three hundred (300) species of plants as an adult insect. The beetles are "skeletonizers," leaving a net-like pattern of leaf veins in the wake of their chewing. Grape and rose are among their favorites.

Typical "skeletonizing" damage by Japanese Beetle

Japanese beetles are classified as scarab beetles, in the family Scarabaeidae, subfamily Rutelinae, collectively known as the shining leaf chafers. The adults become suddenly abundant about mid-summer. They fly well, quickly dispersing themselves over the landscape. Their sheer numbers, the telltale pattern of damage they do to foliage, their size, and their behavior help to make them easy to identify with a little practice.

Japanese Beetles congregating and mating

These are smaller insects than you might expect, ranging from 8.9-11.8 millimeters in body length. That is less than half an inch. They vary in color by individual and age, but most are shining metallic green and red. The flanks of the abdomen are adorned with tufts of white hairs, a feature no other lookalike beetle has. The elytra (wing covers) are striated (have grooves), which also helps set them apart from similar beetles. The hind legs are long and stout, with sharp spurs coming from the tip of the tibial segment (think "shin"). When disturbed, Japanese beetles will flare their hind legs out and up, presenting their spiked weaponry. They can give you a good prick should you insist on seizing one.

Japanese Beetle in defensive pose

The antennae of adult Japanese Beetles are short, with a series of leaf-like plates at the tip, typical of all scarab beetles and their allies. The term for this style of antenna is "lamellate" for "plate-like." The plates are covered in receptors that are tuned to species-specific pheromones for locating others of their kind. Pheromone traps, sold commercially, work well if your goal is to draw even more Japanese Beetles to your yard or garden. Hand-picking the insects and drowning them in pails of water, with a dash of dish soap to break the surface tension, may be the best way to control them. Time consuming for certain, but highly specific to the target pest, and otherwise environmentally friendly.

Green June Beetle, Cotinis nitida

The number one victim of mistaken identity in the Japanese Beetle game is far and away the innocuous Green June Beetle, Cotinis nitida, another scarab beetle that is native to the United States. This insect is much larger, at 15-27 millimeters in size. It is mostly matte green with some degree of iridescence in the right light, especially on the insect's underside. It may or may not be marked with ochre trim, and lines on the wing covers. You may hear these beetles before you see them, as they fly loudly. Green June Beetles, and their relative, the Fig Beetle (Cotinis mutabilis), are classified as "flower chafers" in the subfamily Cetoniinae. They have a special hinge on each wing cover that allows the elytra to remain closed while the membranous hind wings are deployed for flight. Consequently, flower chafers bear a great resemblance to large bees while cruising around looking for food or mates. Green June Beetle feeds on flower nectar and pollen, but occasionally damages ripe fruit; and they also feed on fermenting sap from wounds on trees. This makes them a mild pest under circumstances of orchards and nurseries. As grubs, Green June Beetles feed on decomposing organic matter. You will often see females diving headlong into compost and manure heaps to lay their eggs. In nature they look for rich humus.

Emerald Flower Scarab

Another flower chafer sometimes mistaken for a Japanese Beetle is the Emerald Flower Scarab, Euphoria fulgida. This beautiful beetle measures 13.4-19.8 millimeters. It is often highly active and quicker to fly than the other beetles mentioned so far. It varies considerably in color according to both the individual and the geographic locality it lives in. Specimens from the foothills of the Front Range in Colorado, for example, are deep purple and brilliant turquoise.

Dogbane Leaf Beetle

Recently, I had a....disagreement with someone in social media about the identity of yet another beetle, the Dogbane Leaf Beetle, Chrysochus auratus. At 8-13 millimeters, it approximates the size of a Japanese Beetle. It is superficially colored the same, too, being brilliant metallic green, red, blue, bronze, or copper, depending on the angle of light hitting the creature. That is where the similarity ends. The Dogbane Leaf Beetle belongs to a completely different family, the Chrysomelidae. One look at the long, uniformly segmented antennae, tells you it is not a scarab. Its legs are not armed with spines or teeth, and it has cute, wide little feet for gripping plants. Most decisive, however, is the food preference for this species. Dogbane Leaf Beetle feeds only on....surprise....dogbane. You may occasionally encounter an individual that has alighted on some other plant in the course of trying to find a mate or another dogbane plant, but there will never be large numbers of them on anything but dogbane.

Female Tiphia wasp searching for buried scarab grubs

All manner of control strategies have been applied to the Japanese Beetle, yet here it is, still with us, in arguably greater numbers than ever, and steadily expanding its empire. We have imported the Spring Tiphia wasp, Tiphia vernalis, from China in 1925, a natural enemy. The female wasp digs up a beetle grub, stings it into temporary paralysis, lays an egg on it, and abandons it. The larval wasp that hatches feeds on the grub externally, eventually killing it. We also employ Bacillus popilliae, known better as "milky spore disease" to combat the grubs. The bacterium turns the beetle larvae a milky white color in the process of killing them, but it also affects native scarab grubs.

A large robber fly, Laphria lata, has skewered a Japanese Beetle on its proboscis

Be careful in how you control Japanese Beetles, lest you adversely impact garden allies. Assassin bugs, particularly the Wheel Bug, and robber flies, are among the chief predators of Japanese Beetles, but they need as natural a landscape as possible to proliferate and be effective controls. Invasive species are an artifact of global consumerism, and coveting thy (foreign) neighbor's flora. Resist the temptation and help prevent the next pest from gaining a foothold.

Nope, not a Japanese Beetle. Not even a beetle, but the nymph of a Green Stink Bug.

Sources: Evans, Arthur V. 2014. Beetles of Eastern North America. Princeton, New Jersey: Princeton University Press. 560 pp.
Ratcliffe, Brett C. 1991. The Scarab Beetles of Nebraska. Lincoln: University of Nebraska. Bulletin of the University of Nebraska State Museum, vol. 12. 333 pp.
Berenbaum, May R. 1995. Bugs in the System: Insects and Their Impact on Human Affairs. New York: Addison-Wesley Publishing Company, Inc. 377 pp.
Fahmy, Omar. 2007. "Species Tiphia vernalis - Spring Tiphia,"
Eaton, Eric R. and Kenn Kaufman. 2007. Kaufman Field Guide to Insects of North America. Boston: Houghton Mifflin. 392 pp.


  1. Wish I had read this earlier today, before we saw a large green bug that now I think was a June bug!

  2. I still like the traps, just place them away from your plants. I put a couple out this last weekend and literally watched them draw the Japanese beetles out of my garden to the traps.
    Even if they draw from the neighborhood it will still be less beetles left to mate.

  3. Those pheromone traps have a big range. I rember using them as a kid near a soybean field when they got real bad one year. Filled multiple giant black trash bags. They never stopped either. Seemed to draw in a never ending supply of those things. Gave up on those traps. In a way, they were too effective.


Blog author currently unable to reply to reader comments, nor comment himself. Working to resolve this.