The Tent Worm Swarm

They’re here, they’re everywhere, and they’re ecologically important.

Article and photos by Megan Nichols

If you live in an area with wild cherry (Prunus spp.), you have probably noticed a swarm of these fuzzy caterpillars this month. The Eastern tent caterpillar, Malacosoma americanum, is performing its yearly swarm. These caterpillars start in the canopy of their cherry hosts, where they form a communal silk tent (hence the nickname “tent worm”). At night, they leave the tent and eat the branches bare. When the larvae are ready to pupate, they come down from the trees and search for a place to settle.

They do this en masse. The ground becomes awash in caterpillars for a couple weeks as they run around looking to climb upward. They climb trees, lawn furniture, and people who stand still too long. They go everywhere.

Within a week or so, the swarming slows to a stop. Tent worms produce only one generation a year. In a few weeks the successful caterpillars will metamorphose into moths that will lay eggs in the branches of the cherry trees. Those eggs will lay dormant until the next spring.

Given the very salient habits of this caterpillar, it is not shocking that they are considered a nuisance to many. A Google search of this caterpillar will pull up methods of eradication, ranging from puncturing the webs to burning them off the tree. Yet for those who value a healthy ecosystem in their yards, these insects should be valued. The trait which makes them a nuisance are the same that make them valuable; they are a plentiful food source.

From birds to insects, many small, native predators thrive during this swarm. Nesting birds collect caterpillars off the branches and bring them to their chicks. Ants drag dead caterpillars underground. Wasps bury them in their nursery burrows. During the time of offspring, these caterpillars are there. They are food for the young of many. They may defoliate your cherries, but they are invaluable to the habitat.

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