Don't fear the creepy crawlys


Staff writer

It looks like a scene out of a horror flick.

White webs engulf the branches of ornamental fruit trees, circling up the trunks from the grass below, filling the Ys of the branches. The denuded limbs bear fluffy white tufts, like cones of cotton candy or the fake Halloween spider webbing used for decorating haunted houses.

Writhing within the webs are famished Eastern tent caterpillars which devour the leaves in preparation for their transformation into moths later in the summer.

They rate high in “ee-ew factor,” but the moths themselves aren’t harmful to trees or people and don’t pose a threat of overrunning Federal Way or cocooning great sections of parks in their webs, according to local experts.

Jennifer Schroder, director of the city’s Parks Department, said the tent caterpillars tend to have a large breakout every seven years. “This is one of those years,” she said.

Elaine Anderson, of the Washington State University Master Gardeners program of King County, said tent caterpillars become more and more populous over the years until they reach a critical mass, at which point natural predators, including the pachinid wasp and a particular virus, take over and trim their populations back to a manageable number. Tent caterpillar populations also are dependent on environmental factors, like food and weather.

Their life cycle is fairly rapid, with the eggs hatching in early spring from egg cases laid on tree branches. The larvae begin to spin the webs, eventually covering several branches, and the caterpillars eat the leaves and grow.

While they seem to take over a tree, neither Anderson nor Schroder have heard of a tree fatality caused by tent caterpillars. The caterpillars eat all the foliage and make the tree unattractive, but they don’t burrow into the bark or root system.

Around June — or earlier, if the weather’s nice — the caterpillars begin dropping from the trees and spinning cocoons on blades of grass, in the ground or “wherever they land,” Anderson said. Ten days later they emerge as moths and, shortly thereafter, they mate. By late summer or early fall, the moths find new host trees on which to lay their eggs and then they die.

Tent caterpillars prefer deciduous trees. Anderson said if there’s webbing in a conifer, it’s probably not from a tent caterpillar.

Though they’re a harmless, natural part of the environment, they can be a pest and they can cover a tree, like in four ornamental fruit trees at Dumas Bay Center in Federal Way. And it’s no fun to have caterpillars dropping from trees onto decks, walkways and porches.

The most environmentally friendly way to get rid of tent caterpillars is to prune the branch they’re on, put it in a plastic bag and seal it, and put it in the garbage. For the less environmentally inclined or for large infestations, hardware and home-improvement stores carry pesticide sprays that target tent caterpillars.

Schroder doesn’t recommend the old-fashioned remedy of dousing the webs in gasoline and burning them. “It’s not a good idea,” she said. “It’s not safe.”

In isolated areas of the city, parks department crews ignore the tent caterpillars. “It’s part of nature and we let it go,” Schroder said.

However, if the trees are an ornamental element in a landscaped area or an infestation would pose a nuisance to neighbors, maintenance workers will spray the caterpillars. Workers were out two weeks ago to spray the caterpillars on the trees at Dumas Bay Center.

Staff writer Erica Hall: 925-5565,

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