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Malacosoma disstria

Forest tent caterpillars. Photo: Tawny Simisky
Scientific Name: 
Malacosoma disstria
Common Name: 
Forest Tent Caterpillar
Growing Degree Days (GDD's): 
192–363 GDD's, Base 50F, March 1st Start Date (Source: Cornell Cooperative Extension.)
Host Plant(s) Common Name (Scientific Name): 
Ash (Fraxinus spp.)
Basswood (Tilia spp.)
Birch (Betula spp.)
Blackgum (Nyssa sylvatica)
Elm (Ulmus spp.)
Hawthorn (Crataegus spp.)
Oak (Quercus spp.)
Poplar (Aspen spp.)
Sugar maple (Acer saccharum)
Sweetgum (Liquidambar spp.)
Willow (Salix spp.)
Insect Description: 

The forest tent caterpillar is native to Massachusetts and North America. Unlike its common name suggests, it does not build a tent. Egg masses (1/2 to 1.5 inches long) overwinter and are similar to those of the eastern tent caterpillar (Malacosoma americanum) in the sense that they are wrapped around host plant twigs and coated in a shiny substance (spumaline). The main difference is that the ends of the forest tent caterpillar egg masses are square in shape, whereas the eastern tent caterpillar egg masses are tapered. Eggs hatch in the spring and the caterpillars migrate to the canopy of the tree, in search of expanding flower and leaf buds to feed on. Larvae continue to feed on the foliage of their host plants as it becomes available. They will feed together in groups when caterpillars are still small, but may wander individually as they mature. Caterpillars may reach up to 2 inches in length and are blue and gray with oval white spots down the back that are sometimes described as "key holes" or "tiny penguins". Pupation occurs after they spin pale yellow cocoons in folded leaves attached to plants or buildings. Adults are tan colored moths, approximately 1.6 inches long with two dark brown stripes on each forewing. Moths are active in the late afternoon and at night and are attracted to lights. One generation of forest tent caterpillars occurs per year.

Damage to Host: 

The forest tent caterpillar can periodically be a significant defoliator of deciduous trees in its native range. However, population outbreaks typically soon collapse due to naturally occuring parasites, predators, and pathogens that regulate forest tent caterpillar populations. Depending upon the size of the population, partial to complete defoliation of hosts can occur. Young caterpillars may cause shothole-like damage to leaves prior to complete defoliation by the larger caterpillars. Small populations of forest tent caterpillars may be tolerated. While tree growth may be inhibited following a forest tent caterpillar outbreak, tree death is not usually observed. (Not without other contributing factors.) This is an early season defoliator.


The forest tent caterpillar does not make a large obvious web like the eastern tent caterpillar or fall webworm. Look for shotholes in deciduous plant leaves early in the spring. Large caterpillars tend to feed at night and hide near the ground during the day.

Cultural Management: 

Remove egg masses from twigs of favored host trees prior to hatch.

Natural Enemies & Biological Control: 

There are many parasites, pathogens, and predators of the native forest tent caterpillar which are likely responsible for maintaining low populations of this insect, with the exception of the occasional outbreak. There are several species of parasitic wasp, as well as the fly Sarcophaga aldrichi, which resembles a large house fly and is often noticeably abundant during outbreaks. Pathogens such as Entomophaga aulicae and a nucleopolyhedrosis virus (NPV virus) also regulate forest tent caterpillar populations.

Chemical Management: 

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Bacillus thuringiensis subsp. kurstaki (NL)

Beauveria bassiana (NL)

Bifenthrin (NL)

Carbaryl (L)

Chlorantraniliprole (NL)

Chlorpyrifos (N)

Chromobacterium subtsugae (NL)

Cyantraniliprole (NL)

Cyfluthrin (NL)

Deltamethrin (L)

Emamectin benzoate (L)

Flonicamid+cyclaniliprole (N)

Gamma-cyhalothrin (L)

Horticultural oil (L)

Indoxacarb (L)

Insecticidal soap (NL)

Lambda-cyhalothrin (L)

Malathion (L)

Methoxyfenozide (NL)

Neem oil (NL)

Permethrin (L)

Pyrethrins+sulfur (NL)

Spinetoram+sulfoxaflor (N)

Spinosad (NL)

Tau-fluvalinate (NL)

Tebufenozide (NL) 

Zeta-cypermethrin (L)


Active ingredients that may be applied systemically include: acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), chlorantraniliprole (soil drench), cyantraniliprole (soil drench, soil injection), emamectin benzoate (injection), and neem oil (soil drench).

When used in nurseries, chlorpyrifos is for quarantine use only.

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: .