Forest tent caterpillar (FTC) (Malacosoma disstria) is native to North America and can be found throughout New York State. Sugar maple trees are the caterpillar’s preferred food source, along with aspen, cherry, and apple. Despite its name, FTC does not build a tent, and instead creates silken mats on branches and trunks where caterpillars gather.
Description
- Egg Masses: Forest tent caterpillar egg masses are shiny, brown cylindrical masses about half an inch long and are found wrapped around branches in the canopy.
- Caterpillars: FTC reach approximately two inches in length when fully grown. They have dark brown to black-colored bodies and light blue heads. They have light blue lines down their sides with a series of white footprint-shaped marks down their back. These markings distinguish them from spongy moth and eastern tent caterpillars, which may be found together and are sometimes confused
- Moths: The caterpillar spins a cocoon, from which a tan or light brown moth with two dark stripes on its wings emerges.
Look-alikes
Tent caterpillars look similar to spongy moths and also feed in the spring. However, unlike the non-native spongy moth, tent caterpillars are native species and are an important food source for a number of bird and other wildlife species.
| Comparison Chart | ||||
|---|---|---|---|---|
| Forest Tent (Native) | Eastern Tent (Native) | Fall Webworm (Native) | Spongy Moth (Non-native) | |
| Eggs | Dark compact cylindrical mass with square ends, encircling the branch. New masses are shiny without holes. Old masses are dull and show exit holes. Deposited around small twigs in July. Masses may contain up to 350 eggs, average 150 in NY. | Dark compact cylindrical mass with tapered ends encircling the branch. New masses are shiny without holes. Old masses are dull and show exit holes. Deposited around small twigs in July. Masses contain up to 350 eggs. | Light green or yellow hair covered patches about the size of a dime on the underside of leaves. Contains 100 – 1000 eggs.
| Tan-colored or lighter fuzzy patches (masses) on tree trunks, branches, firewood, or in a sheltered spot, even on lawn furniture. Usually 600-700 eggs/mass. |
| Egg Mass |
Image Credit Steven Katovitch, Bugwood.org |
Image Credit David L. Clement, University of Maryland, Bugwood.org |
Image Credit Pennsylvania Department of Conservation and Natural Resources - Forestry, Bugwood.org |
Image Credit William M. Ciesla, Forest Health Management International, Bugwood.org |
| Larvae (caterpillar) appearance | Dark with light blue lines down sides and line of white "footprints" down back. Light blue heads. Fully grown is about 2 inches long. | Dark with white line down back with light blue and black spots on sides. Black head. Fully grown is about 2 - 2 ½ inches long. | Pale yellow to dark grey, with yellow spots and long and short bristles. There are two cream stripes along the sides. | Five pairs of raised blue spots followed by six pairs of raised red spots along back. Fully grown is about 2 inches long. |
| Caterpillar |
Image Credit Johnny N. Dell, Bugwood.org |
Image Credit William M. Ciesla, Forest Health Management International, Bugwood.org |
Image Credit Milan Zubrik, Forest Research Institute - Slovakia, Bugwood.org |
Image Credit Steven Katovich, Bugwood.org |
| Larvae behavior | Hatch at bud break in spring. Tend to migrate to treetops. Feed on opening buds and new foliage one branch at a time. Young larvae are gregarious, often group together, follow each other in a line, and form silken mats on trunk, branch or leaves where they gather, rest and molt. Older larvae are nomadic foragers even prior to complete defoliation. | Hatch at bud break in spring. Congregate in obvious silken tents in branch forks. Feed on opening buds and new foliage in colonies. Use tent to rest and as protection from extreme temperatures, rain, birds and other predators. Larvae leave the tent to feed. Fully grown larvae leave the host tree to find a protected place to pupate. | Eggs hatch in late June or early July. Young larvae feed in groups on the undersides of leaves. Webs are typically found at the ends of branches. All caterpillar activity occurs within this webbing, which becomes filled with leaf fragments, cast skins, and frass. Fully grown larvae wander from the webs to pupate | Hatch when oak buds are opening. Younger larvae chew small holes in the leaves. Older larvae feed from the outer edge of the leaf toward the center. Will feed until tree is stripped, then go in search of food. When feeding will leave behind noticeable frass (droppings). When populations are sparse, larvae feed at night, crawling down the trunk to hide in a protected spot during the day. When populations are dense, feeding occurs day and night. When tree is stripped, larvae go in search of new food sources. |
| Pupa | Solitary cocoons, pale yellow silk in folded leaves or protected areas | Solitary cocoons, white silk with yellow powder | Dark brown, 10 mm long, thin cocoon made of silk and debris overwinters in protected areas such as the leaf litter where they will remain for the winter. | Hard brown case, pointed at one end in sheltered location |
| Adult moths | Light brown with two narrow dark bands/stripes on the forewings. Lay eggs on hosts. Strongly attracted to light. Sexes look similar. | Reddish brown with two white stripes on forewings. Sexes look similar. | Generally white but can have dark spots on the wings. Considered a hairy moth, has white and brownish orange hair on its body. | Females do not fly. Females are white with brown markings. Males are brownish. |
| Adult |
Image Credit Mark Dreiling, Bugwood.org |
Image Credit Lacy L. Hyche, Auburn University, Bugwood.org |
Image Credit Mark Dreiling, Bugwood.org |
Image Credit USDA APHIS Plant Protection and Quarantine, USDA APHIS PPQ, Bugwood.org |
| Most common host trees | Sugar maple, aspen, cherry, apple, oaks, birch, ash, alder, elm, basswood and willow. Does not feed on red maple, sycamore or conifers | Mostly cherry, apple, and crabapples, also other fruit trees ash, birch, maple, oak, poplar, and occasionally pecan, hawthorne, beech and willow | Cherry, apple, birch, walnut, ash, maple | Oaks preferred. Also apple, sweetgum, speckled alder, basswood, gray and white birch, poplar, willow and others. Avoid ash, yellowpoplar, sycamore, black walnut, catalpa, locust, American holly, and shrubs such as mountain laurel, rhododendron and arborvitae. Older larvae will also feed on conifers such as hemlock, pines, spruces and southern white cedar. When populations are dense, larvae will feed on almost any tree and shrub. |
Cyclical Outbreaks
Population numbers vary over the years from very few and not noticeable, to many and very noticeable defoliation (loss of leaves). FTC outbreaks typically occur every 10-15 years and usually last 2-3 years. Outbreaks are usually ended by natural causes such as disease and predators.
One such predator is the friendly fly (Sarcophaga aldrichi), known for hanging around people and landing on them. This predator’s population grows fast when FTC populations outbreak. Friendly flies deposit their larvae in FTC cocoons; the larvae then feed on and kill the FCT before it can emerge as an adult moth. While they can be a nuisance, friendly flies do not bite and are harmless humans.
The previous outbreak began in 2005 and lasted through 2009, with heavy defoliation occurring from the southern Catskills across central New York and northward to St. Lawrence County.
Impacts
FTC begin feeding on new spring leaves as trees leaf out and continue through June. Healthy trees can survive 2-3 repeated years of defoliation (loss of leaves). Trees defoliated early in the season often grow a new, smaller set of leaves in July once FTC are done feeding. However, defoliation reduces a tree’s overall resilience and ability to withstand stress, resulting in slower growing trees that are more susceptible to environmental impacts (such as droughts or floods), pests, and diseases. Stress caused by defoliation can result in mortality 8-10 years after the defoliation event as some trees are unable to withstand multiple stressors.
Management
When deciding whether to manage FTC, consider the extent and severity of the outbreak as well as the overall health of the trees:
- Healthy trees can often withstand a single defoliation event and re-leaf later in the season.
- Trees already stressed by drought, disease, site conditions, or repeated defoliation are more vulnerable to decline and may benefit from protection.
Most management options are better suited for protecting high-value trees or localized FTC infestations. If treatment is needed to meet management goals, such as protecting high-value trees, maintaining newly established plantings, or preserving important seed sources, there are options.
Management is not practical for controlling widespread outbreaks. Additionally, FTC populations are naturally controlled by insect predators, diseases, and wildlife including birds and rodents, making treatment unnecessary.
DEC and its partners typically do not manage FTC, and treatments are usually limited to ecologically or culturally significant forests. DEC does not provide funding for controlling FTC on private property.
Mechanical Treatment
Mechanical (non-chemical) management options for forest tent caterpillar are focused on small trees and ornamentals, but not practical for forest-scale control.
Egg masses can be removed by pruning or scraping them from branches before they hatch in spring. After hatch, small larvae can be handpicked from plants and knocked into a bucket of soapy water for disposal. Alternatively, larvae on smaller trees can be sprayed directly with soapy water.
Sticky bands may also be placed around trunks to capture FTC caterpillars as they move up and down trees. They are most effective when applied before caterpillars hatch (late winter to early spring) and again in late summer to early fall to prevent egg-laying females from reaching the canopy. These bands can be bought or made at home using common household materials. View detailed instructions on how to make and use your own trap on the University of Wisconsin website. These barriers must be checked and replaced frequently to remain effective.
Insecticide Treatment
Microbial insecticides are biopesticides made from naturally occurring bacteria, viruses, fungi, or protozoans that can be targeted to a specific pest. The most common of these is Bacillus thuringiensis (Bt), which occurs naturally in soil and on plants. The Bt subspecies kurstaki (Btk) is the most appropriate to use for FTC control. It is safe to use around people, animals, and plants, but it does affect young moth and butterfly larvae and can kill other species of caterpillars besides FTC. When Bt is eaten, the caterpillar becomes paralyzed, stops feeding, and dies of starvation or disease. If you are considering spraying, start planning in fall or winter as many of these services book up early. Spraying is not effective against pupae or egg masses and is less effective once caterpillars reach 1 inch long.
Woodlot Recommendations
To minimize additional stress on trees, delay timber harvests in defoliated areas for two or three years after an outbreak. Recently defoliated trees are susceptible to root diseases so root damage caused by harvesting equipment should be avoided. Time will also allow you to see which trees remain healthy or need to be salvaged and to alter harvesting plans if necessary.
Conduct FTC Surveys
You can survey your woodlot or forest to determine the likelihood of FTC defoliation for the next growing season. This can be done when egg masses are present, approximately August through April but is most easily done October through February when there are no leaves on the trees. The surveys typically take 20 minutes to 1 hour to complete, depending on population numbers.
Field Protocol for Surveying Forest Tent Caterpillar Egg Masses (PDF)
