Eastern tent caterpillar nests are often created where branches meet the stem.
Photo by William H. Hoffard, USDA Forest Service, Bugwood.org.
In the spring, just as the leaves are starting to expand on trees, silken webs sometimes appear on tree branches and stems – they start small, then gradually increase in size until they can be several inches across. At first glance, these may look like spider webs, but they are actually made by the eastern tent caterpillar (Malacosoma americanum). These caterpillars hide in the tents for protection during the day and exit the tent to feed on leaves at night. Their feeding can sometimes result in nearly total tree defoliation. Damage caused by eastern tent caterpillars is usually just aesthetic, but the stress caused by defoliation can make trees more vulnerable to other damaging agents. Eastern tent caterpillar tents are most often observed on fruit trees, like cherry, apple, and crabapple. In South Carolina, you may notice the nests or hairy caterpillars in the late spring and early summer.
Identification and Life Cycle
Eastern tent caterpillar adult female moths lay clusters of 150 to 400 dark, shiny eggs around small twigs. These egg masses overwinter and hatch in early spring, just as leaves are starting to expand. Small, hairy caterpillars that emerge from the eggs are mostly dark with white stripes and two thin, yellow stripes along the top of their bodies. Throughout the spring, groups of these caterpillars feed and grow in their tents to avoid being eaten by predators and other natural enemies. The caterpillars are gregarious, meaning many individuals share a single tent-like nest throughout their development.
Eastern tent caterpillar egg masses are dark in color and located on small twigs.
Photo by Beatriz Moisset, commons.wikimedia.org.
Breaking open an eastern tent caterpillar tent will reveal a mass of caterpillars.
David Coyle, ©2024, Clemson Extension
Unlike other tent-building species, eastern tent caterpillar tents are dense and built in the fork of branches. In comparison, fall webworms build tents on the ends of branches and ailanthus webworms build sparse tents within the foliage on Ailanthus trees (also called tree of heaven).
Older caterpillars grow to 1 – 1 ½ inches long with blue, yellow, and black mottling and a large white stripe down the top of their body. In late spring or early summer, mature caterpillars leave their tents to spin silky, yellow to white colored cocoons. After pupation, fluffy light brown moths emerge. These adults have two light horizontal stripes across each wing, and they will start the cycle over by mating and ling egg masses around small tree branches.
Mature eastern tent caterpillars have a distinct white stripe down their back.
Photo by the Pennsylvania Department of Conservation and Natural Resources – Forestry, Bugwood.org
Adult moths are brown in color.
Photo by Andy Reago & Chrissy McClarren, commons.wikimedia.org
Hosts and Damage
Eastern tent caterpillars typically infest fruit trees, including apple, cherry, peach, plum, and pear. Occasionally, caterpillars will build tents in other deciduous trees, such as maples. Since eastern tent caterpillar eggs hatch in the early spring, leaves can be eaten just as buds are breaking. Defoliation from the eastern tent caterpillars rarely causes more than aesthetic damage; however, large outbreaks or repeated years of defoliation can cause mortality in young trees or make trees more susceptible to other damaging agents.
The hairs on the caterpillars can cause eye and mouth irritation, so handwashing after handling or using protective gloves if handling them is recommended. Additionally, these caterpillars may cause reproductive harm when consumed by horses (referred to as mare reproductive loss syndrome), so horse owners should monitor host trees for signs of eastern tent caterpillars.
Thin lines of webbing may be visible on trees with eastern tent caterpillar tents; these tents are typically where the branch meets the main tree stem.
David Coyle, ©2024, Clemson Extension
Management
While eastern tent caterpillars rarely kill trees directly, they can negatively impact tree health and aesthetics through defoliation and can occasionally cause mortality in young trees or during large outbreaks. For efficient management, homeowners can remove egg masses manually with a hand pruner. Caterpillar tents can be manually removed and destroyed, or simply ripped open with a stick to allow natural enemies to access the caterpillars hiding inside. Promoting natural enemies, such as birds, stink bugs, and wasps, can help manage tent-building caterpillar populations. For additional information on natural enemies, see Incorporating Beneficials Into the Gardener’s Toolkit. Webs should never be burned on the tree, as this will cause more damage to the tree, and the fire can easily spread out of the desired area.
If necessary, pesticides can be used to control caterpillars. Applying bacterial-based insecticides, such as Bacillus thuringiensis (Bt) or Spinosad, to the foliage near tents can control younger caterpillars. Other pesticides labeled for caterpillar control may be used on older caterpillars. Please consult your local Clemson Extension agent prior to use, and always read and follow the instructions on pesticide labels.
Originally Published 11/24
