Forest Tent Caterpillar Damage Expected Again in 2017

Forest tent caterpillars have hatched, according to forest health specialists from the Vermont Department of Forests, Parks and Recreation. The insect is expected to cause widespread defoliation this summer, mostly in forests across northeastern and central Vermont.

Forest tent caterpillars are native to North America, and prefer eating leaves on sugar maple and ash over other tree species. The tree damage caused can significantly reduce tree growth and impact maple tapping for Vermont sugarmakers, which contribute $140 million annually to the state’s economy.

In 2016, forest tent caterpillars defoliated 25,000 acres of forestland in the state. Most trees survive defoliation, even if they are defoliated several years in a row, but a significant outbreak can cause trees to die off.

Over the past winter, the Department of Forests, Parks and Recreation conducted surveys of forest tent caterpillar egg clusters in more than 60 actively tapped sugarbushes to predict the risk of defoliation for 2017.

Based on these surveys, landowners will have 18 of these sugarbushes treated with a biological insecticide, Bt, to protect them from defoliation. Bt (or Bacillus thuringiensis) is allowed for certified-organic production of agricultural products.

Natural enemies of the caterpillar have brought previous outbreaks to an end before significant tree mortality occurred. Approximately 3,600 acres of forest will be treated in mid-May to early June as a precaution, when the forest tent caterpillars are actively feeding.

In spite of their name, forest tent caterpillars do not create “tents” of webbing like their close relatives, the eastern tent caterpillars. The insects are mostly blue, with white keyhole-shaped spots.

To learn more about the forest tent caterpillar and previous efforts to monitor and predict their populations in Vermont, go to:

Contact: Barbara Schultz, Forest Health Program Manager, 802-777-2082