Under any other circumstances, we might admire their striking metallic green and bronze uniforms and their tenacious grip.
But Japanese beetles are back this year in astonishing numbers. They're gobbling up linden tree leaves, rose bushes and vegetable gardens, and they're hooking up with each other at a furious rate.
Steve Black, who started a tree nursery this year in Adamstown, near Frederick, likens the infestation at his farm to a biblical plague. "I have them clustered six deep on trees they supposedly don't like," he said. "It's unbelievable."
Brian Brannan, the garden shop manager at Valley View Farms in Cockeysville, called it "the worst Japanese beetle season I've seen in probably the 17 years I've been here."
Homeowners have made a run on his stock of insecticides and beetle traps. "We've sold an average of 100 traps each year, but this year we've sold 500," he said.
Even entomologists are impressed.
"It's Japanese beetle heaven out there," said Mike Raupp, a professor of entomology and a cooperative extension service specialist at the University of Maryland College Park.
He attributes the backyard population explosion to ample rain across the region during the past two summers. That kept the soil moist and boosted the survival rates of two generations of beetle eggs and grubs.
The grubs have munched happily on the roots of our lawns each fall and again the following spring. And now they've emerged again as an even bigger horde of airborne adults determined to feed in our gardens and to mate.
Out in the heat
If the summer rains produced a lush feast, July's high temperatures brought them to the table. "The heat made everybody come out all at once and synchronize early," Raupp said. "The beetles are just going nuts out there now."
It wasn't always this way. The Japanese beetle - Popillia japonica - is an exotic species, a hitchhiker from Japan that first appeared in the United States in a southern New Jersey nursery in 1916.
Since then, despite some efforts to eradicate them, the beetles have spread to 22 states east of the Mississippi River, plus Iowa, Missouri, Wisconsin and isolated spots in California and Oregon.
Lovers of linden
These immigrants found a bountiful menu here, feeding on more than 250 different species of plants. They eat the soft parts of the leaves and avoid the harder veins, leaving behind a mere skeleton of a once-healthy leaf.
And they have a special taste for linden trees.
"You'll be driving down the road and see linden trees lining the road with lots of defoliation," said UM entomologist Paula M. Shrewsbury, an extension service specialist in ornamental plants and turf issues. The damage turns the trees a rusty brown.
The beetles also fancy apple and crabapple trees, Japanese and Norway maples, pin oaks and birch. They avoid magnolias, red buds, dogwoods, red maples and northern red oaks.
While healthy trees will bounce back from the damage, ornamental plants and vegetables might not. Commercial nurseries, orchards, and turf and vegetable farms can sustain significant losses.
The beetles aren't a big problem in Japan, where natural enemies keep them in check. But in North America, predators and parasites have a tougher time keeping up.
Parasitic wasps called scoliids and tiphiids manage to sniff out the beetle grubs where they live buried in the soil. When they find some, the female wasps dig into the dirt and lay their eggs in the grubs' bodies.
When those eggs hatch, the larval wasps become "ectoparasites," feeding on the beetle grubs' body fluids, eventually killing them.
"It's really quite dramatic, a bounty for the tiphiids and scoliids," Raupp said. (Homeowners can encourage these wasps by planting peonies, which attract them.)
Birds, squirrels, chipmunks, toads, microscopic worms and other pathogens also have taken a liking to the beetles. But just how well they're able to limit beetle numbers is not known, Raupp said.
They certainly haven't kept up with this year's infestation. It's cresting now, and the adult bugs should be gone in two weeks or so.
But the beetle boom will resume next summer unless a drought between now and then cuts into the survival rates of eggs and grubs in the soil, Raupp said - or unless populations of natural enemies catch up and begin to tip the scale.
"Then we'll begin to see beetle populations go down again," he said.
But we're not there yet. Black, the nurseryman from Adamstown, said he saw two sweet gum trees "just black with beetles." A few days later, those trees were stripped of their green and the swarms had moved to the next trees in the row.
He expects his trees to survive, but he's not yet sure how much money he'll lose if they take longer to reach market size as a result.
The beetles are crawling out in Washington County, too. Donna Tedrick, 63, of Clear Spring, said they nearly destroyed one of her apple trees.
"It happened overnight," she said.