Tent Caterpillars

The Culprit: “Tent” Worms

Easily recognized by the large silk tents, or webs, that the larvae construct during the spring in the crotches of trees, particularly apple and cherry trees. Tent caterpillars are hairy and usually brightly colored, with blue and yellow spots. Periodically they become serious orchard pests and occur in large enough numbers to defoliate whole trees and damage the fruit. Many larvae live gregariously within the tent, which they use for shelter during the night and in rainy weather. During the day, the larvae leave the tent and feed on the leaves in nearby branches.

The best-known tent maker is the Eastern tent caterpillar, Malacosoma americanum. In addition to being an orchard pest, it has been linked to mare reproductive loss syndrome (MRLS), in which apparently healthy mares experience high rates (more than 70% in experimental studies) of aborted fetuses or stillborn foals. An outbreak of MRLS resulted in the lost of more than 5,000 foals in Kentucky in 2001. Elimination of caterpillar populations, by removing host trees or eradicating the caterpillars, or otherwise avoiding horse contact with the caterpillars and their waste appears to prevent the syndrome. Other species of Malacosoma occur both in E and W North America and have been known to defoliate large areas by attacking a variety of forest and shade trees. Not all species build tents; despite the name forest tent caterpillar, M. disstria, at times an extremely destructive pest that migrates by the millions to new food plants, never weaves a tent.

What to Do About it: Removing egg masses during the winter or removing tents in the early spring and soaking them in kerosene or burning them, are the most effective means of control.