Under the gray, misty November sky covering Panthertown Valley near Cashiers, we swish through shin-deep leaves in search of hemlock trees. 

Mature hemlocks typically exceed 50 feet and can be more than 100 feet tall, but there are no towering giants in Panthertown Valley anymore. The hemlocks we do find scattered along the trail are mostly small and scrawny, an abundance of bare branches intermingled with those bearing short, green needles.

Arrival of the adelgid

That’s the fault of an invasive insect called the hemlock wooly adelgid, said hike leader Charles Dial, an entomologist working for the N.C. Department of Agriculture and Consumer Sciences’ Plant Industry Division. Dial, who led the hike on behalf of Friends of Panthertown, hopes that the trail will yield evidence of beneficial bugs at work, chewing toward an end to the adelgid’s destructive reign.

“We’re hoping that we can get it in a harmonious balance and keep the adelgid population down,” Dial told the group. “They won’t go to zero, but keep them low enough population that they’re not killing our trees, allowing the hemlock to come back.”

A vial contains specimens of a beetle species that has been released to prey on the adelgid. Holly Kays photo

Originally from Japan, the hemlock wooly adelgid was first reported in the eastern United States in 1951 near Richmond, Virginia. Since then, it has spread to at least 20 states, feeding exclusively on native hemlock trees. The adelgid goes dormant during the warmest part of the year and is most active in the winter, as it prepares to lay its eggs. After hatching, the insects affix themselves to the base of the hemlock needle, feeding on the tree’s starch reserves and prompting the tree to respond like it would in the face of a severe drought — pulling back on new growth and, in the case of older trees, putting out more cones.

“Usually, the adelgid moves on because it likes the new growth to start feeding on,” Dial said. “But as soon as the tree recovers slightly, they’re back.”

This continued stress means that the adelgid’s presence amounts to an eventual death sentence for hemlock trees in eastern North America. Adelgid populations are down this year after the sudden freeze around Christmas 2022 killed many of them — but because the introduced population reproduces asexually, it easily recovers from such setbacks.

Hemlocks were once ubiquitous on the banks of mountain streams, especially headwater streams. Their roots kept soil from eroding, their shade kept trout waters cool and their cones and needles provided food for wildlife. Now, with the exception of those that have received chemical treatment, all the big hemlocks are gone.

Seeking solutions

It’s not like that in the adelgid’s native Japan, or in the northwestern United States, where a population of hemlock wooly adelgids has lived since at least the 1920s, when their presence was first recorded. It’s disputed whether that population is native or was introduced long ago. In both regions, the adelgid lives alongside natural predators that keep its population in check.

As Appalachian forests fill with fallen giants, researchers are engaged in a race against time, pursuing multiple strategies to save these majestic trees. Though it’s not a practical approach on a landscape scale, chemical treatment can keep individual trees safe from the adelgid, and experimentation continues on certain forestry practices that may give hemlocks an edge. Some researchers are taking a genetic approach to the problem, using gene splicing or breeding hemlocks with adelgid-resistant traits to develop a line of trees capable of holding their own.

But biological control — introducing insects that prey specifically on the adelgid — is another promising area of study, and that’s what Dial came to Panthertown to discuss. He holds up a stick and a white square of canvas, held flat with a wooden frame. It’s called a beat sheet. The plan is to hold it underneath any adelgid-infested trees we come across, hit the branches above with the stick, and search the sheet for insects.

“You don’t realize that there are millions of insects everywhere all the time,” Dial said.

Among those millions of insects, he hopes, will be the three species of beetles that have so far been released to combat the adelgid.

The longest-used beetle, a natural hemlock wooly adelgid predator from Japan called Sasajiscymnus tsugae, was first released in Connecticut in 1995. More recently, two beetle species in the genus Laricobius have made it through the extensive process required to approve them for general release. L. nigrinus, which preys on hemlock wooly adelgid populations in the Pacific Northwest, was cleared for release in the eastern part of the country in 2000, while Japan native L. osakensis was first released in 2012. Research is currently underway on an additional predator, the silver fly, which if cleared for release is expected to feed on the hemlock wooly adelgid during the late spring and summer months — a time of year when the three beetle species are not active.

The idea, Dial said, is to create a complex of predators that together can exert enough pressure on the adelgid to knock it down to the level of the countless other Appalachian species that feed on the region’s trees without threatening their survival.

Hope for the future

We walk through mist along the mountainside from the Salt Rock Gap Trailhead to Blackrock Mountain, then descend the slope to return along the valley floor. When we approach a hemlock tree, no matter how small, Dial pauses and checks the underside for the telltale white fuzz of adelgid egg sacs. If he finds it, he gets out the beat sheet. 

“I’m looking for a little half grain of rice,” he says, peering at the scattered fragments of debris on the sheet. There’s dirt, hemlock needles, bits of bark and occasionally a fly or spider. But none of the beetles Dial hopes to see.

Charles Dial (far right) and hike participants look for Charles Dial (far right) and hike participants look for hemlock wooly adelgids in Panthertown Valley. Holly Kays photo

We pause at Salt Rock, a dramatic overlook whose focal point is Big Green Mountain and the accompanying edifice known as the Great Wall of Panthertown. All the trees are bare, the sky still gray. The only spots of color are the evergreens dotting the landscape — these days, they’re nearly all pine, not hemlock. Dial takes advantage of the pause to investigate a couple other small hemlocks along the edge of the overlook. But no luck.

He’s not discouraged, though.

“Today was I guess as much as anything just a little talk and demonstration about some of the things we do,” he said. “It wasn’t really a serious, all-day survey.”

In a serious survey, Dial said, he’d be “tapping like crazy,” from at least three different places on every hemlock tree he spotted. He’s done such surveys in Panthertown before and once found several S. tsugae there. They may well still be around, though there’s a continual need for more data.

The hemlock’s future is uncertain, but Dial is hopeful that a solution is on the horizon. Someday, future generations may know what it is to stand in the cool shade of a hemlock grove on a hot summer’s day, listing to the ripples of a nearby mountain stream.

The hemlock wooly adelgid was first found in the eastern United States The hemlock wooly adelgid was first found in the eastern United States in 1951. Holly Kays photo

Give hemlock researchers a hand

Help out hemlock researchers during a volunteer day 10 a.m. to 4 p.m. Tuesday, Dec. 12, in Waynesville.

Volunteers will support the work of the Forest Restoration Alliance by helping out with tasks in the greenhouse and nursery where FRA is breeding hemlock trees that are resistant to the hemlock wooly adelgid. Researcher Ben Smith will give a tour of the facility as part of the event.

To participate, contact Caroline Lord at outreach@savehemlocksnc.org  or 828.252.4783. The deadline to sign up is Thursday, Dec. 7. Space is limited.