Tent Caterpillars: Pests That Defoliate Trees 

Tent caterpillars are distributed widely in tropical and temperate regions. These caterpillars, Malacosoma spp. (Lepidoptera; Lasiocampidae), get their Latin name from “malakos,” meaning “soft,” and “soma,” meaning body. The common name of the tent caterpillar is derived from the tent-like silk structure built by larvae on tree branches.  

Tent caterpillars are distributed in Eastern and Western Europe, India, China, Japan, and Russia. In North America, six species of tent caterpillars are found (see Table 1). The forest and Eastern tent caterpillars occur in Georgia.  

Tent caterpillars are defoliators of a wide range of host plants, including hardwood and fruit trees. The presence of these caterpillars, their frass (droppings), and damage is a nuisance and reduces the aesthetic appearance of trees and shrubs. Although this pest does not directly kill trees, defoliation during outbreaks causes branch dieback and reduces growth, ultimately leading to tree death.

Table 1. Tent Caterpillar Species Found in North America.

Common name	Scientific name
Forest tent caterpillar	Malacosoma disstria
Eastern tent caterpillar	Malacosoma americanum
Western tent caterpillar	Malacosoma californicum
Southwestern tent caterpillar	Malacosoma incurvum
Pacific tent caterpillar	Malacosoma constrictum
Sonoran tent caterpillar	Malacosoma tigris

Description 

Tent caterpillars lay eggs in masses, and these shiny, dark brown or black egg masses encircle the stem or twig of a tree (Figure 1). Newly hatched caterpillars (Figure 2) are 3 mm long, black, and have fur-like setae on their bodies.

The coloration, markings, and patterns on the late stages of caterpillars vary by species. The late-stage Eastern tent caterpillars (ETCs) are black with blue and white markings and a continuous white line on a black background (Figure 3).

Forest tent caterpillars (FTCs) are similar in appearance to ETCs, except they have white dots instead of a continuous white line on their backs (Figure 4).

Western tent caterpillars (WTCs) have a blue-white stripe with black bands along the body (Figure 5). 

In the spring and early summer, most tent caterpillars build a tent-like structure with silken webbing among the branches of trees (Figure 6).

In contrast, forest tent caterpillars construct a silken mat on leaves. The tent covers the larvae, protecting them from predators, such as birds. It also helps shield them from harsh weather conditions—allowing them to adapt to extreme heat (providing thermoregulation)—and assists with larval molting. 

Life Cycle  

All tent caterpillars have a similar life cycle and complete one generation in a year. Tent caterpillar adult females lay only one egg mass each annually. An egg mass of 100–350 eggs can be seen encircling twigs in mid-summer. Egg masses overwinter and hatch in April and July in the southern and northern U.S., respectively, which coincides with local trees’ leaf expansion.  

Colonies of first-instar caterpillars stay together and spin a silken web around a branch junction or on trunks. Instead of tents, forest tent caterpillars produce a silken mat on branches or trunks where the caterpillars rest. The caterpillars from the first to fourth or fifth stages are gregarious and feed on foliage. The size of the tent increases as the caterpillars grow. The tent serves as a rest area for the caterpillars. They leave the tent during the day for food and return at night.  

The last larval stage becomes solitary in habit, wanders off, and feeds individually. Tent caterpillars develop through five to eight larval stages. Additional larval stages are added if they feed on poor-quality tree materials, allowing them to reach the optimal size for pupation. Larval development is completed within 4 to 7 weeks.  

Late-stage caterpillars pupate inside silken cocoons located in bark crevices, on leaves, in the ground, and under any structure (Figure 7).

Moths emerge from those cocoons in May or June to July in the southern and northern U.S., respectively.

The adult moths of various tent caterpillars have different colors: yellowish in FTC (Figure 8), brown in ETC (Figure 9), and black to greyish in WTC (Figure 10).

Damage  

Tent caterpillars feed and defoliate their plant hosts from early April to late June. During pest outbreaks, defoliation (Figure 11) causes branch dieback, growth reduction, and occasionally kills the tree.

If the population is abundant, tent caterpillars may strip the trees and migrate to new tree hosts. The tent, colonies of caterpillars (Figure 12), and silken cocoons on trees and shrubs reduce the aesthetic appearance of landscapes.  

Host Range  

Tent caterpillars have a wide host range. Forest tent caterpillars feed on trees such as trembling aspen (Populus spp.), alder (Alnus spp.), birch (Betula spp.), cherry (Prunus spp.), sugar maple, oak (Quercus spp.), elm (Ulmus spp.), basswood (Tilia americana L.), water tupelo (Nyssa aquatica L.), blackgum (Nyssa sylvatica Marshall), and sweetgum (Liquidambar styraciflua L.), and feed on shrubs such as willow (Salix spp.).

Eastern and Western tent caterpillars feed on black cherry, apple, crabapple, pear, and some other fruit trees. WTC also feeds on shrubs, including bitterbrush (Purshia tridentata), California lilac (Ceanothus spp.), mountain mahogany (Cercocarpus spp.), and some other ornamental shrubs. 

Management  

In ornamental landscapes, such as in residential or commercial settings, tent caterpillars can be managed by destroying egg masses in the winter, as these are visible on defoliated trees when the eggs are laid on lower branches. Developing tents can be physically destroyed as new tents appear on trees. The tent caterpillars also can be trapped using a sticky collar wrapped around the tree trunk to capture migrating caterpillars. In residential areas, caterpillar colonies and cocoons can be dislodged by using high-pressure water sprays.  

Several insecticides are effective on tent caterpillars. Microbial insecticides, such as Bt products (Bacillus thuringiensis var. kurstaki), spinosad, and baculoviruses, are effective against the younger stages of tent caterpillars. Insect growth regulators, such as diflubenzuron, can be used. However, diflubenzuron is not recommended for use near water, as it can harm aquatic arthropods.  

Biorational insecticides such as azadirachtin and insecticidal soap effectively reduce tent caterpillar populations. Synthetic insecticides, such as organophosphates (malathion and acephate), pyrethroids (permethrin and bifenthrin), and carbamates (carbaryl), are also effective on larvae, and they can be spot-applied. Younger larvae are more susceptible to insecticides than caterpillars in the later stages.  

All insecticides should be used according to the label.  

References  

Batzer, H. O., & Morris, R. C. (1978). Forest tent caterpillar. U.S. Department of Agriculture, Forest Service. https://www.fs.usda.gov/foresthealth/docs/fidls/FIDL-09-ForestTentCaterpillar.pdf 

Ciesla, W. M., & Ragenovich, I. R. (2008). Western tent caterpillar. U.S. Department of Agriculture, Forest Service. https://www.fs.usda.gov/foresthealth/docs/fidls/FIDL-119-WesternTentCaterpillar.pdf 

Cooke, B. J. (2024). Forest tent caterpillar (Lepidoptera: Lasiocampidae) across Canada, 1938–2001: I. Periodic outbreaks; episodic impacts. The Canadian Entomologist, 156, e8. https://doi.org/10.4039/tce.2024.4 

Dellinger, T. A., & Day, E. (2025). Eastern tent caterpillar (Publication No. 444-274, ENTO-622NP). Virginia Cooperative Extension. https://www.pubs.ext.vt.edu/444/444-274/444-274.html 

Fitzgerald, T. D. (1995). The tent caterpillars. Cornell University Press. https://doi.org/10.1017/S0007485300041444  

Fitzgerald, T. D., & Willer, D. E. (1983). Tent-building behavior of the Eastern tent caterpillar Malacosoma americanum (Lepidoptera: Lasiocampidae). Journal of the Kansas Entomological Society, 56(1), 20–31. http://www.jstor.org/stable/25084365 

Ruiu, L., Mannu, R., Falchi, G., Braggio, A., & Luciano, P. (2013). Evaluation of different Bacillus thuringiensis sv kurstaki formulations against Lymantria dispar and Malacosoma neustria larvae infesting Quercus suber trees. Redia, 96, 27–31. https://www.researchgate.net/publication/266016156_Evaluation_of_different_Bacillus_thuringiensis_sv_kurstaki_formulations_against_Lymantria_dispar_and_Malacosoma_neustria_larvae_infesting_Quercus_suber_trees  

Schowalter, T. D. (2017). Biology and management of the forest tent caterpillar (Lepidoptera: Lasiocampidae). Journal of Integrated Pest Management, 8(1), 24. https://doi.org/10.1093/jipm/pmx022