Eastern Tent Caterpillars and Forest Tent Caterpillars on Trees
Eastern tent caterpillars on crabapple. Photo: David L. Clement, University of Maryland, Bugwood.org
Updated: March 14, 2024
Key points
Silk webs of the Eastern tent caterpillar are a common sight in early spring on their preferred hosts, cherry and crabapple trees.
Impacts from Eastern tent caterpillars are primarily aesthetic because some people consider the tents unsightly. They do not typically substantially damage or kill trees unless the trees are small and repeatedly defoliated.
Groups of caterpillars make a web (or tent) in a crotch where tree branches fork. They hide within the web at night to avoid predators, cold, and rain.
These native caterpillars are an important part of Maryland food webs and provide early-season food to predators such as birds.
If you wish to control caterpillars, egg masses can be easily scraped off of twigs during the winter.
Eastern tent caterpillars (scientific name Malacosoma americanum) are native insects to Maryland. They can be found all over the eastern United States and southern Canada. These caterpillars are gregarious (meaning they feed in groups) and can grow as large as 2” (5 cm). They are boldly patterned with black, orange, white, and blue colors. Mature caterpillars have a distinct white stripe down their backs. Long setae (hairs) cover their bodies. Hundreds of individual caterpillars can live together in a single tent.
Forest tent caterpillars (Malacosoma disstria) have a similar lifecycle and appearance. However, these caterpillars only make silk mats when they molt, not full tents like their cousins. Fall webworm (Hyphantria cunea) is another gregarious, web-making caterpillar species. They are active later in the summer and into fall. Tent placement can be used to differentiate them: Fall webworms build on the ends of tree branches, whereas Eastern tent caterpillars build in branch crotches.
Eastern tent caterpillars turn into moths. As adults they are light brown with two cream-colored bands across their wings. They are very hairy--almost furry looking--and about 1” (2 cm) long. Adults can be seen flying in May and June and are attracted to lights.
Comparison of species and their nests
Comparison of Similar Species
Forest tent caterpillar (left) has keyhole-shaped white spots; Eastern tent caterpillar (right) has a white stripe. Credit: Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, CC BY 3.0 US DEED
Eastern Tent Caterpillar Nest
Eastern tent caterpillars build silk nests in branch crotches in early spring. Photo: Steven Katovich, Bugwood.org, CC BY 3.0 US DEED
Fall Webworm Tent
Fall webworm caterpillars build nests that cover the ends of branches in late summer and fall. Photo: G. Keith Douce, University of Georgia, Bugwood.org, CC BY 3.0 US DEED
Life cycle
Eggs are contained in a 1” long, black, gall-like mass. It is usually laid on a slender twig (see photo below). The mass has a protective covering that feels like styrofoam.
Larvae develop within a few weeks but stay dormant inside their eggs through the winter.
Depending on weather conditions, the eggs hatch around the first week of April in central Maryland. This may even occur before wild cherry buds have opened.
Young caterpillars are completely black.
After a few days, they start spinning a silk tent, which they enlarge as they grow.
Tents are formed in “crotches” where tree branches fork.
Caterpillars hide in the tent, emerging only to feed.
Most feeding damage is done in May by the large caterpillars that mature by the end of May.
When they finish feeding, they leave the trees to seek hiding places where they can spin protective cocoons.
The small brown moths emerge from cocoons in early summer and mate to produce the overwintering eggs.
Apple, cherry, and crabapple (plants in the Rosaceae family) are preferred hosts for the Eastern tent caterpillar. If caterpillars run out of leaf tissue on their original host, they can wander off and eat many other woody plants.
Because the Eastern tent caterpillar is a gregarious species, feeding damage is concentrated in a small area. This can mean defoliation of branches or entire trees. Usually, damage from Eastern tent caterpillars happens so early in the season that trees can regrow leaves and fully recover. However, if trees have been recently planted or are otherwise stressed, repeated defoliation can be enough to kill them.
Eastern tent caterpillar populations naturally cycle, so outbreaks only happen about once every 10 years. While defoliation in outbreak years is a serious concern for orchards, damage caused by caterpillars in urban and suburban trees is primarily aesthetic. Some consider the large silken webs unsightly. Tents are obvious on a tree’s bare branches in early spring, and they can persist in the tree long after the caterpillars are gone.
Horse breeders should be aware that accidental ingestion of Eastern tent caterpillars has been linked to mare reproductive loss syndrome. Caterpillar setae (hair) can irritate a horse’s digestive tract and introduce bacteria into the bloodstream, causing infections that may lead to fetal death. Preventing horses from grazing near cherry trees and/or muzzling during outbreak years is recommended.
Cultural control
Scrape egg masses off twigs during the winter.
Prune or rip out tents on cold or wet days (when caterpillars are inside).
If tents are out of reach, they can be removed with a pole with protruding nails or a pressurized hose.
Caterpillars can be easily crushed or drowned in water.
Removing nearby wild cherry trees is not recommended because Prunus species are important native food sources for all kinds of wildlife, including over 450 species of caterpillars.
Eastern tent caterpillar egg mass. Photo: Brian Kunkel, University of Delaware, Bugwood.org, CC BY 3.0
Biological control
Conservation biological control is very effective for this species because a large variety of animals consume this native caterpillar.
Birds are one of the Eastern tent caterpillar’s natural enemies and many species serve as predators on their eggs, larvae, and adult moths.
Yellow-billed and black-billed cuckoos have been found to pursue caterpillar outbreaks and feed on all sizes of larvae. They will eat 200 caterpillars in a single meal.
Insects are also natural predators of Eastern tent caterpillars, with Calosoma ground beetles and stink bugs being the most common. Other natural insect enemies include lady beetles, assassin bugs, and paper wasps.
127 species of parasitoid wasps and flies have also been found to attack Eastern tent caterpillars.
Chemical control
In cases where cultural and biological controls aren’t sufficient and repeated years of defoliation occur, chemical controls can be applied. They are most effective when applied early in the season when caterpillars are small.
Apply Bt (Bacillus thuringiensisvar.kurstaki or aizawai) as soon as the silk tents are observed in early spring. It must be sprayed on leaves the caterpillars will eat. Bt should be applied early in the season since only young caterpillars (less than 1”) are highly susceptible to this insecticide. It is available under many trade names, including Thuricide and DiPel.
Other reduced-risk insecticides include chlorantraniliprole (trade name Acelepryn) and spinosad. They can be applied directly on caterpillars and on leaves the caterpillars will eat. The application can happen later in the season when caterpillars are slightly larger but should penetrate the tents to be effective.
USE INSECTICIDES WITH CARE. READ THE LABEL DIRECTIONS. FOLLOW ALL SAFETY PRECAUTIONS. Mention of trade names does not constitute an endorsement by University of Maryland Extension.
Revised by Yasmine Helbling, Kelsey McGurrin, and Dr. Karin Burghardt, University of Maryland Department of Entomology, March 2024
