Malacosoma americanum

Eastern tent caterpillar. Photo: Tawny Simisky
Scientific Name: Malacosoma americanum
Common Name: Eastern Tent Caterpillar
Growing Degree Days (GDD's): 90-190 GDD's, Base 50F, March 1st Start Date. (Source: Cornell Cooperative Extension)
Host Plant(s) Common Name (Scientific Name)
Apple (Malus spp.) *Preferred host.
Ash (Fraxinus spp.)
Birch (Betula spp.)
Blackgum (Nyssa sylvatica)
Cherry (Prunus spp.)
Crabapple (Malus spp.) *Preferred host.
Maple (Acer spp.)
Oak (Quercus spp.)
Peach (Prunus persica)
Plum (Prunus domestica)
Poplar (Populus spp.)
Wild cherry (Prunus avium) *Preferred host.
Willow (Salix spp.)
Witch-hazel (Hamamelis spp.)
Insect Description:

This is a native defoliating insect in the United States. Large populations of this insect occur in outbreaks approximately every 8-10 years. This insect overwinters in the egg stage. Eggs are laid in masses of 150-350. These masses encircle small twigs, have rounded edges, and are a dark gray with a shiny coating. Larvae hatch from these egg masses in the spring, well timed with the opening of wild cherry leaves. Larvae work in groups, gathering at branch crotches and begin to build a web which will grow in size as the caterpillars continue to feed. Fully grown caterpillars are hairy, basically black in color with a long white line down the back with smaller yellow lines and blue spots. Once mature, the caterpillars disband from the web and seek appropriate shelter to pupate, spinning a white cocoon around themselves. Pupation may occur on host plants, fences, and other objects. Adult moths emerge in late-June, early-July and are reddish brown with white stripes on their forewings. One generation occurs per year. This insect is often confused with the forest tent caterpillar (Malacosoma disstria) which does not construct a web/tent.
Damage to Host:

Mostly defoliators of wild cherry, crabapple, apple, lilac (source: Bob Childs), cotoneaster (source: Robert Childs, UMass Extension), and others. Makes silken webs in crotches of branches which can be unsightly. 
Monitoring:

Scout for egg masses prior to hatch in the spring. Scout for still-small tents from the early hatched caterpillars if the egg masses are missed.
Cultural Management:

Prune out egg masses on twigs prior to hatch and destroy. Remove webs by hand, especially when still small and caterpillars have not done too much feeding. DO NOT burn webs still attached to the host plant!
Natural Enemies & Biological Control:

Parasites of this insect are usually effective. There are occasional outbreaks (every 8-10 years) and spot infestations in landscapes. Several natural enemies of the eastern tent caterpillar exist, including birds, small mammals, insect predators, and parasitic wasps.
Chemical Management:

Abamectin (NL)

Acephate (NL)

Azadirachtin (NL)

Bacillus thuringiensis subsp. kurstaki (NL)

Bifenthrin (NL)

Carbaryl (L)

Chlorantraniliprole (NL) 

Chlorpyrifos (N)

Chromobacterium subtsugae (NL)

Cyfluthrin (NL)

Deltamethrin (L)

Emamectin benzoate (L)

Gamma-cyhalothrin (L)

Indoxacarb (L)

Insecticidal soap (NL)

Lambda-cyhalothrin (L)

Malathion (L)

Methoxyfenozide (NL)

Permethrin (L)

Pyrethrins (L)

Pyrethrins + piperonyl butoxide (L)

Spinetoram+sulfoxaflor (N)

Spinosad (NL)

Tau-fluvalinate (NL)

Tebufenozide (NL)

Zeta-cypermethrin (L)
Notes:

Larvae leave webs on warm days to feed; foliar applications are said to work best at this time. Otherwise, caterpillars may be protected from contact insecticides when found inside their webs.

Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), azadirachtin (injection, soil drench), and emamectin benzoate (injection).

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: September 27, 2024. To check current product registrations in Massachusetts, please visit the MA Department of Agricultural Resources Pesticide Product Registration page and click on "Search Pesticide Products Registered in Massachusetts - Kelly Solutions".