LONGVIEW — They’re everywhere up here, and they’ve brought the elements of an insect horror movie to the upper Toutle Valley.
The Hummocks Trail near Coldwater Lake is speckled with their brown, fuzzy bodies, and you can’t help squashing them by the dozen as you hike the terrain northwest of Mount St. Helens. They’ve turned the trunks of trees into wiggling, squirming masses. If you briefly stand still, several will creep up your boots and legs. Interpretive signs and kiosks are curtained with their writhing bodies, and if you stand silent you can hear them munching away at the leaves of red alder trees.
A breakout of tent caterpillars that began last summer has exploded this year at the heart of the volcano’s blast zone. Billions and billions of inch-long critters are stripping alders of foliage and bringing a creepy, but fascinating new factor to the evolution of the landscape Mount St. Helens blasted 32 years ago.
Later this summer, after the caterpillars emerge from cocoons, the air will be filled with clouds of white, creamy moths.
Tent caterpillars, like many other species of insect, typically experience boom-and-bust cycles, according to ecologists and entomologists. These cycles depend on the weather, food availability, the status of predators and other factors.
However, no one knows why caterpillar numbers surged last year and are really mushrooming this year, said Peter Frenzen, chief scientist for the U.S. Forest Service-managed Mount St. Helens National Volcanic Monument. Nor is there any way to determine whether the outbreak could be related to climate change, which has been cited as a factor in the pine beetle forest kill that is fueling massive fires in the Rocky Mountain states.
Scientists don’t, however, expect the tent caterpillar outbreak here to have such calamitous effects.
“From what I’ve read, this should be a three-to-five year cycle. We should see an increase in the population until their food supply and/or disease causes the population to crash,” Frenzen said.
Robert Michael Pyle, an award-winning nature writer and entomologist from Grays River, said boom-and-bust insects like tent caterpillars typically “eat themselves out of house and home and parasites increase and then they collapse. … It’s an absolutely natural thing for them.”
Because they are a native species, and the Volcanic Monument was established to allow natural processes to occur without human interference, the Forest Service does not plan to institute any controls, Frenzen said.
For now, the caterpillars are eating almost exclusively alder, a pioneering plant that is the dominant tree species in the area because it grows in the sterile volcanic debris that buried the valley floor hundreds of feet deep. There’s some indication, Frenzen said, that caterpillars are also eating blackberry bushes.
How the caterpillars affect the landscape is an intriguing question Frenzen is hoping some researcher looks into.
He and Pyle doubt the caterpillars will kill the alders, which grow rapidly and should put on new foliage once the caterpillar spin cocoons, a process that turns them into moths. Usually, foliage-eating insects typically don’t destroy their host plants, Pyle noted.
However, the caterpillars could kill off some struggling alders and thereby give more light to other species, Frenzen speculated. In addition, the caterpillars’ droppings could also act as a fertilizer for other plants and trees, such as the Douglas fir, Pacific silver fir and other conifer species that now dapple the landscape.
“If you’re an alder in the shade and already stressed, this may push you over the edge. Naturally thinning will occur,” Frenzen said. “If you’re a Doug fir or hemlock hanging around in the understory, this would be a good thing because it will mean more light and more nutrients.”
So, it’s possible the caterpillar could play a role in determining the nature of the forest that emerges. Certainly their presence will attract songbirds and other predators to the areas, Pyle said.
“You never have that much fat and protein in one place without something wanting to eat it,” he said.
Once the caterpillars turn into moths, they’ll be an ample food supply for bats, “which are under great stress,” he added.
Only time will tell whether the caterpillars play a major evolutionary role in shaping the future of the landscape, a process scientists called “succession.”
“As an event in the natural succession, this could be a significant one,” Frenzen said. “It is an event that might explain something later.”