Beneath the treetops of Rocky Gap State Park, Maryland is breeding an army of predator beetles born to hunt a vampiric pest that is killing the forest’s eastern hemlocks.
The size of a sesame seed, Laricobius nigrinus, with its exploitable taste for an invasive sap-sucker, has become a star of the Maryland Department of Agriculture’s Forest Pest Management Program.
In recent years, the state has propagated enough beetles to share its supply with other states that are also battling the uninvited guest — the hemlock woolly adelgid, or HWA.
Left alone, HWAs can slowly bleed a grove of the flat-needled evergreens dry, leaving behind towers of sticks and wiping out the mini ecosystem that relies on the tree. In Maryland, there are an estimated 42,000 acres of hemlock groves.
Each year, Maryland invites other states with infestations to collect L. nigrinus during peak harvest, which typically falls between late October and early November.
That’s when L. nigrinus beetles wake up from their long summer naps beneath the forest soil. They emerge hungry and just as their only food source, HWAs, are at their most sedentary — and perhaps most juicy — life cycle phase.
Hemlocks’ heroes
Led by program entomologist Patrick Simons, foresters from the Ohio Department of Natural Resources embarked on their first bug harvest one recent Friday morning.
Armed with sticks and square canvas sheets, roughly the size of a kite, they split off into the woods and start turning over evergreen branches. To find L. nigrinus they must first find its food.
The HWAs they’re seeking are as tiny as the period ending this sentence. But their secretions, a white, waxy fluff, gives them away. The protective cottony blob surrounds the adult and its eggs, while its mouth, a piercing, straw-like tube, taps the root of a single pine needle and drains the tree of nutrients.
Simons said there’s a working theory about L. nigrinus’ singular palate. They may have developed a taste for the mold that grows on the HWAs “honeydew” — another word for its gooey bug poop. But over time, they ditched settling for poop mold and decided to eat the whole bug.
Using a method called beat sheet sampling, the foresters lightly tap the HWA-laden branches with their sticks, catching whatever falls in their canvas kites.
Simons sifts through a diorama of forest life. Among the tiny spiders, moths, needles and sticks in his sheet he spots one black L. nigrinus. Simons uses an aspirator attached to a pill bottle and sucks up the beetle, soon to be a Buckeye.
Simons will later wipe debris and any hitchhikers from the dozens of beetles caught that day with the dry bristles of a watercolor paintbrush, ensuring only L. nigrinus cross state lines.
This extraordinary effort is about more than fending off one parasitic bug. It’s also about saving the menagerie of microorganisms, bugs, birds, fish and amphibians reliant on hemlock groves for their habitat.
“It’s a big messy, interconnected web of everything, growing and eating and doing their thing,” Simons said.
Since hemlocks grow well in shade and their thick needles can block out the sun, the air temperatures beneath its branches can be 5 to 10 degrees cooler than a deciduous tree forest.
“There’s not really another tree that grows quite in the same way, and there’s not really a replacement for it,” Simons said.
Streams running through hemlock groves tend to be cooler too, creating a chill climate for brook trout and an endangered salamander, called the eastern hellbender. Certain bird species prefer nesting in hemlock branches and populations decline when HWAs take over.
One of Simons’ favorite hemlock dwellers is the thread-legged bug. With bodies similar to walking stick bugs, their thin, featherweight legs allow them to walk across a spiderweb and eat the spider without getting stuck in the sticky silk.
A predator appears
Native to Asia, the hemlock destroyer was first spotted in British Columbia in the 1920s. They then appeared in Virginia in the 1950s and Maryland roughly 30 years later.
L. nigrinus has defended Maryland’s hemlocks against them for generations.
The Forest Pest Management Program brought L. nigrinus from the West Coast in the early 2000s in partnership with the U.S. Forest Service’s Hemlock Wolly Adelgid Initiative. Simons credits Forest Health Specialist Biff Thompson for championing Maryland’s program and facilitating the first release in 2004 in Rocky Gap State Park.
So far this year, foresters and other volunteers from a handful of states have harvested Maryland’s L. nigrinus to release back home. Roughly 35,000 Maryland beetles have been exported to states along the Eastern Seaboard. Some of those beneficiaries, such as Rhode Island, have begun propagating their own supplies.
While the expansion of the chemical-free pest control tool is promising, eradicating the well-established HWAs isn’t likely, nor is it the goal, Simons said. What’s more realistic is to suppress them.
The good news? Hemlock woolly adelgids are slow eaters. It can take as long as 14 years for a tree to succumb to infestation, Simons said.
Otherwise, hemlocks can live for hundreds of years. Some of the state’s oldest are found in Garrett County’s Swallow Falls State Park and can grow 60 to 70 inches in diameter.
It’s hard to objectively measure the program’s success, he said. But the fact there are so many eastern hemlocks still thriving in Maryland is a good sign the HWAs aren’t winning.
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