WILLIAMSTOWN, MASS. - About two weeks ago, the center of town experienced a population explosion of two caterpillar species - the forest tent caterpillar with a single row of white dots running down its back, and the related Eastern tent caterpillar which has two rows of white dots. Both will eventually turn into little brown moths.
According to a campus memo from Horticulturist and Grounds Supervisor Dave Fitzgerald, the recent spraying of selected trees with Bacillus thuringiensis (Bt) has failed to control the outbreak. A second round of caterpillars has emerged and the footprint of the infestation has grown.
After consultation with college biologists and with an expert on the forest tent caterpillar at the University of Massachusetts, the College has decided to begin spraying the parts of campus most necessary for the upcoming Commencement and Reunion activities with a product called Conserve SC.
The active ingredient in Conserve SC is spinosad, an organic neurotoxin. After the caterpillars come in contact with the substance or ingest it, they die in two to three days. While Conserve SC is considered safe, college officials plan to apply it as sparingly and carefully as possible.
Spraying will begin Thursday, May 25, and continue at least through Friday. Fitzgerald's memo stated that campus buildings would be informed which areas would be treated when and asked to close building air intakes as appropriate. Treated trees will be marked with larger signs than were used during the Bt spraying.
More extensive treatment of the entire campus and College-owned faculty and staff housing would pose a serious risk of environmental and health effects.
After the spraying the college plans to clean caterpillars off of sidewalks, steps, handrails and other surfaces of caterpillars.
In untreated areas the caterpillars will continue their search for leafy food for the next few weeks before spinning their cocoons, from which they will re-emerge in mid- to late June for their brief few days of life as moths. Fitzgerald stated that the infestation is a natural occurrence, and that the trees that have been eaten should send out a second round of leaves later in the growing season.
But the worst may be yet to come. Williams biology professor Hank Art was quoted in a recent Williams Record article as warning that an outbreak of invasive gypsy moth caterpillars, which are larger than tent caterpillars with red and blue spots and long bristles, might occur after their eggs hatch in late May.
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