Inchworms attack trees, shrubs in Eagle River

Posted: Thursday, July 08, 2010

ANCHORAGE - Chomping inchworms are stripping the leaves off native trees and shrubs in parts of the Eagle River area. Homeowners are calling insect experts looking for answers. At high elevations, the infestation has left pockets so gray and bare the landscape looks like spring never came.

University Of Alaska Fairbanks Cooperative Extension Service
University Of Alaska Fairbanks Cooperative Extension Service

In the affected areas, "it's quite dramatic. I mean there's complete defoliation. Everything is stripped bare," said Michael Rasy, an Anchorage-based pest management technician for the University of Alaska Fairbanks Cooperative Extension Service.

Rasy and other experts say the critters are part of the large geometrid family of caterpillars and moths, he said.

The larvae are commonly called inchworms or loopers because of how they loop up, then stretch out as they crawl along.

They are tiny, a half inch to an inch.

Scientists are still trying to definitively identify the species but think two may be involved, neither of which is common in Alaska. One type is dark or striped and the other is fluorescent green.

So far it's unclear why their population exploded along Birdsong Drive, off Hiland Drive, and then extended to points higher.

Maybe a mass of eggs was imported into Alaska on landscaping plants.

Maybe the timing was especially favorable and masses of caterpillars hatched just as the trees leafed.

Dwarf birch and willow along the nearby South Fork Valley trail in Chugach State Park were particularly hard hit, Rasy said. When he and an entomologist from the U.S. Forest Service checked out the infestation last week, they found the ground along the trail itself littered with squirming caterpillars looking for a place to pupate, or go through their cocoon stage.

"They are dropping out right now," Rasy said. "In fact, they are just flying through the air on a silken thread. It's getting near the end of the infestation. They are bailing out of the canopy because there is nothing left."

Homeowner Chris Solomonson, who lives on an acre-plus spread on Birdsong Drive at about 1,700 feet elevation, first alerted Rasy to the phenomenon.

One evening during a backyard marshmallow roast a couple of weeks ago, Solomonson's 4-year-old daughter Maya yelled out. The adults investigated and saw little caterpillars wiggling out of the trees on tiny strands of silk.

"They were getting all in her hair and everything," Solomonson said. "She started freaking out."

The mini munching machines were everywhere. Birch trees were being eaten down to the twig. So were willow.

The oddest part, Solomonson said, was the sound.

"You could literally stand by the alder bushes and hear it. You could hear them eating," he said.

Before they spotted the caterpillars, the family thought spring simply was late. They could see the neighbor's house next door and glimpse the South Fork of Eagle River, both usually hidden in the summer by thickets of vegetation.

Even this week, a mountainside to the west is dotted with gray brush instead of the usual palette of summer green.

"It looks like winter," said Rasy, who took photos of the caterpillars in Solomonson's yard.

On one alder bush alone, the family saw hundreds upon hundreds of the critters.

But the favorite meal seems to be willow and birch.

Some of the trees in his yard are skeletons without a leaf. Others have a few leaves up at the top.

Yet some areas of alder thicket barely were nibbled and cottonwood was spared any damage.

The caterpillars tend to eat all of their favored vegetation, then drop down to the next level until there's nothing left, Rasy said.

Besides birch and willow, they seem to like raspberry plants. But these types of caterpillars don't go after garden ornamentals or vegetables, he said.

He collected some of the cocoons and brought them back to his office. He is watching for moths to emerge so that he can identify precisely what is doing all the damage.

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