29 April 2026
Nine days ago I saw the first tentworms on a small choke cherry tree at Raccoon Wildflower Preserve. Since then I expected tents to appear on many trees and am disappointed that they haven’t yet. When they do, yellow-billed cuckoos won’t be far behind.
Eastern tent caterpillars (Malacosoma americanum) are native moths whose mother lays a big batch of eggs on a host tree in the Rosaceae family. The tiny caterpillars form inside the eggs and overwinter until next spring when the tree starts to leaf out. The growing caterpillars emerge and build a communal tent where they shelter during the day. At night they come out to eat the leaves of their host — usually a cherry tree.
Tent caterpillars are delicious to birds and a special favorite of yellow-billed cuckoos (Coccyzus americanus) who are one of the few bird species able to eat hairy caterpillars. Yellow-billed and black-billed cuckoos show up in Pittsburgh when the tentworms do.
The population of tentworms flutuates year to year — from not-so-much to “infestation” — and yellow-billed cuckoos take advantage of this. The cuckoos are nomadic and choose to nest in areas with hairy caterpillar outbreaks, according to the study Invasive Prey Impacts the Abundance and Distribution of Native Predators.
Other birds also take advantage of abundant tentworms. Baltimore orioles eat tentworms.
Blue-gray gnatcatchers use the webbing to bind their nests together.
If you have tentworms in your trees, be patient and let the birds get rid of them. Don’t poison the insects with pesticides lest you poison birds or deprive their nestlings of food.
Meanwhile I’m hoping to find more tentworms soon. Unfortunately the weather will be cold and rainy for the next three days including lows in the 30s. 🙁
Hi Kate,
This is from Wikipedia. Seems the newly laid eggs take a year to emerge.
“Tent caterpillars are among the most social of larvae. The adult moth lays her eggs in a single batch in late spring or early summer. An egg mass contains about 200 to 300 eggs. Embryogenesis proceeds rapidly, and within three weeks, fully formed caterpillars can be found within the eggs. The small caterpillars lie quiescent until the following spring, when they chew their way out of the eggs just as the buds of the host tree begin to develop.”
Bob Machesney
Thank you, Bob. I fixed it.