Invertebrates
Japanese Beetle
Popillia japonica · also called Japanese beetles
Overnight, a rose bush that looked healthy the previous evening turns lacy and skeletal, dozens of metallic green Japanese beetles clustered across its remaining leaves, each one having arrived drawn by chemical signals released by the very first beetle to start feeding.
Overview
The Japanese beetle, Popillia japonica, is a metallic green and copper invasive beetle now established across much of the eastern and central United States after an accidental introduction from Japan in the early twentieth century. Its chemically amplified group feeding behaviour and damaging underground grub stage make it one of the more economically significant insect pests in North America.
Damage that calls in reinforcements
Most plant pests simply feed and move on, but the Japanese beetle’s feeding actively recruits more of its own kind to the same target, turning a single beetle’s modest meal into a coordinated assault capable of stripping a shrub bare within days.
Status
Least Concern, increasing — continuing to expand across North America as an established invasive species and significant agricultural and turf pest.
Japanese Beetle: common questions
Why do Japanese beetles gather in such large groups on one plant?
A Japanese beetle releases volatile chemical compounds when it feeds, and these compounds attract additional beetles to the same plant, meaning damage can escalate quickly once even a single beetle discovers a suitable host, often resulting in dozens of beetles feeding together on one shrub or plant within a short time.
How did the Japanese beetle get to North America?
The Japanese beetle was accidentally introduced to North America in the early twentieth century, most likely arriving in soil surrounding imported nursery plants at a port in New Jersey, and has since spread across much of the eastern and central United States as an established invasive pest.
Do Japanese beetles only damage plants above ground?
No, Japanese beetle larvae, known as white grubs, live and feed underground on grass roots, causing patches of lawn to brown and die, meaning the species causes significant damage both above ground as leaf-eating adults and below ground as root-feeding larvae.
How can you identify an adult Japanese beetle?
An adult Japanese beetle displays a distinctive metallic green head and thorax paired with coppery-bronze wing covers, a combination striking and consistent enough to make the species relatively easy to identify despite its modest, roughly centimetre-long size.