Cold temperatures are the pest's worst enemy. That's why the adelgid have ravaged hemlocks in the south, including Tennessee's Smokey Mountains. The winters are much milder, so the adelgid populations don't get thinned out as much.
Bartgis said temperatures must reach 16 below to significantly affect woolly adelgid populations. He said this year, temperatures barely hit zero in the coldest parts of the Mountain State.
Some pesticides can be used against the adelgid. Workers at Adventures on the Gorge treat their hemlocks with a nicotine-based compound. The chemical shrinks the adelgid's appetite, just as cigarettes work as a hunger suppressant for humans.
"They starve themselves to death," Frantz said.
The treatment appears to be working.
Walking across the tour's first swinging bridge, you can see the first stand of trees Adventures on the Gorge treated against the woolly adelgid. These trees are doing well, with evidence of new growth and healthy green buds on the tips of the branches.
Zeus also was among the first group of Adventures on the Gorge's trees to be treated against the woolly adelgid in 2009. Because of that early intervention, it has never had a bad infestation.
Unfortunately, treatment is extremely labor intensive. Workers have to treat each hemlock individually, by burying pesticide pellets in the ground near the root system or drilling a hole in the tree's bark and injecting the chemical directly into its stem.
Scientists around the country have been trying for years to find widespread treatment against woolly adelgid. So far, they haven't had any luck.
Bartgis said researchers have looked at beetles that might eat the woolly adelgid, but those tests have not been successful.
Brandon said in some stands of hemlock in the eastern United States, one tree is perfectly healthy while those around it are dead, victims of woolly adelgid infestations. Researchers are studying those healthy trees to figure out what made them resistant to attack.
"We really don't have an answer right now," she said.
'About a hemlock'
Hemlocks make up about 1 percent of trees in West Virginia's forests. According to a state Department of Agriculture forest health study in 2010, more than 200,000 acres in the state are at risk for hemlock woolly adelgid infestations.
Tucker County has the highest density of hemlocks in West Virginia, with the trees accounting for 7 to 9 percent of the forests there. Pocahontas and Mercer Counties come in second, with 4 to 6 percent of their woods populated by hemlocks.
Although they're not the most common tree in West Virginia's woods, hemlocks are very important.
"Hemlocks are like beaver. They really affect their surroundings," Bartgis said.
Some birds prefer to nest in hemlocks. The shade from the big evergreens makes their surrounding environments cooler.
"That's important for species that need that cool climate, like brook trout in the stream," Bartgis said.
Adventures on the Gorge co-owner Dave Arnold said he had no idea what woolly adelgid were when the company started planning its zip line course.
It wasn't until an arborist was hired to determine the health of its trees that Arnold learned the hemlocks were in danger.
The company has since built a prevention plan into its business strategy. One dollar of every guest's zip line tour goes toward treating the hemlocks. There are about 5,000 mature hemlocks on Adventures on the Gorge's 40-acre plot.
Workers now have treated more than 1,000 of the trees. The company has spent about $30,000 on treatment, not including some labor costs.
Arnold, a longtime whitewater rafting guide, said the hemlocks along the Gauley River are among his favorite features of the waterway. He said the shady evergreens give the forest an intimate feel rafters just don't get on the New River.
"It makes the Gauley," he said. "These hemlocks create a mood. They create an atmosphere. Any trout fisherman understands it."
Arnold said rafting the Gauley might be a completely different experience 20 years from now, if scientists don't find a way to stop the woolly adelgid.
"Someday we may really have a unique place. If something doesn't change, you're going to have a few small places where hemlocks exist," he said.
The stakes are high. If researchers don't find a way to wipe out woolly adelgid once and for all, West Virginia's forests - already irrevocably changed over the state's history by forest fires, disease and irresponsible human behavior - may never look the same.
And the next generation of explorers will never see a tree like Zeus.