Tent caterpillars are on the move

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“Gross” may be the nicest word to say about western tent caterpillars, now on the move en masse in Sequim yards and orchards to find suitable cocooning sites. But have patience — and a blind eye — for a few more weeks, said Laurel Moulton, WSU Extension Master Gardener coordinator, and the writhing masses will be on their way to becoming moths.


“The infestation usually is a two- to three-year cycle and this is the second year. I’ve heard some say it’s one of the worst and others say it’s on par. It really depends on the microclimate of where you live. I would classify this as a pretty bad year.”


In April and May, eggs that hatched in early spring became 2.5-inch long caterpillars with voracious appetites for the leaves of many tree species, especially those in the rose, birch and willow families. The larvae or caterpillars, mass together to spin silken tents for protection while they gorge themselves on tender leaves. Moulton said each tent contains “dozens to hundreds” of caterpillars and when they have had their fill, they come out of the tents in early June.


“People are upset because the caterpillars’ feedings are done and they start wandering around, dropping on people’s heads, cars and in their yards,” Moulton said. “Once it’s mid-June, they’ll either run out of food where they are or are ready to turn into cocoons. My advice is just to tolerate them because spray isn’t very effective at this stage. People just need to hang on for a couple more weeks.”


But she added, because of Sequim’s several microclimates, the infestation process could be less advanced in some neighborhoods. In that case, Moulton recommends pruning off the branches with the offending tents, putting them in a plastic bag, dousing the tents in soapy water and throwing them bagged in the trash.


Next year, early in the season after the overwintering eggs hatch, Moulton recommends spraying with bacillus thuringiensis, a bacteria rather than a poison that’s toxic to the larvae.


Moulton said unless a tree already is distressed or is young, it will rebound the next year from considerable defoliation. With next year being the third in the cycle, the probability is strong that tent caterpillars will appear again, Moulton said.


“It’s hard to tell if then it will be as bad as this year but by the third year their natural predators will have caught up with them,” she noted.


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