The Japanese beetle, Popillia japonica, is an invasive insect species that causes significant damage to turf and ornamental plants across North America. Accurate identification of its various life stages is crucial for effective management. Recognizing the specific appearance of both the adult beetle and its grub form is the first step in protecting your landscape from its destructive feeding habits.
Visual Characteristics of the Adult Beetle
The adult Japanese beetle is a distinctive scarab beetle, measuring approximately 3/8 to 1/2 inch in length. This small, oval-shaped insect has a body composed of two distinct and brightly colored sections.
The head and the thorax possess a brilliant, iridescent metallic green coloration. This vibrant green is a consistent feature. Contrasting sharply with the green thorax are the wing covers, known as the elytra, which are a coppery-brown or bronze color.
The most definitive characteristic for identifying the adult is a pattern of small, white hair tufts along the sides of its abdomen. There are five distinct patches of white bristles on each side, located beneath the edge of the wing covers. Additionally, two more white tufts are present on the very tip of the abdomen. This arrangement of seven pairs of white tufts distinguishes the Japanese beetle from similar-looking species.
Identifying the Grub Stage
The larval or grub stage feeds on grass roots beneath the soil surface. This larva is a white grub, characterized by a creamy white, soft body and a tan or brownish head capsule. When unearthed, the grub naturally curls into a C-shape.
A mature Japanese beetle grub can grow up to about one inch long before it pupates. While many other beetle species have similar white grubs, the Japanese beetle grub is specifically identified by closely examining its raster. The raster is the pattern of hairs and spines on the underside of the grub’s hind end.
To distinguish it from other common lawn grubs, observe the arrangement of bristles on the raster. The Japanese beetle grub possesses a unique V-shaped pattern of hairs just below the anal slit. This V-shaped grouping separates it from the parallel or scattered hair patterns found on other scarab larvae, requiring close inspection with a magnifying glass.
Distinguishing Japanese Beetles from Look-Alikes
Careful attention to color, size, and the white tufts can prevent misidentification. One frequently mistaken insect is the Green June Beetle (Cotinis nitida). This look-alike is significantly larger than the Japanese beetle, measuring closer to one inch in length.
The Green June Beetle lacks the distinct dual-coloration. Its entire body is typically a velvety green, often with gold or bronze highlights, but without the coppery wing covers of the Japanese beetle. Crucially, the Green June Beetle does not have the defining white hair tufts along the sides of its abdomen. Its grubs also differ, as they primarily feed on decaying organic matter rather than living grass roots.
Another common source of confusion is the Rose Chafer or other smaller, less-shiny scarabs. While the size and general shape may be similar, these species typically have a duller coloration, often a lighter tan or brown. They also lack the metallic green sheen on the head and thorax. The absence of the signature white abdominal tufts is the most reliable way to rule out the Japanese beetle.