Forest Tent Caterpillars

SCIENTIFIC NAME

Malacosoma disstria

APPEARANCE

Forest tent caterpillar adult moths are tan to white-yellow colored with brownish-colored bands on the moth's front wings. In addition, the adult has a series of darker-colored hairs on its abdomen and has a wingspan ranging from 1 to about 2 inches.

When larvae first hatch from their egg case, they are dark-colored and less than 1/8-inch long, but have easily-seen hairs on the body. Larvae stay together and move by following a silk trail deposited by the foraging and feeding file's leader. As they grow and molt into successive larval stages, pale blue lines appear on the sides of the body along with a row of footprint-shaped white spots along the mid-line of the upper portion of the body. These markings become more distinct, as each molt occurs. Fully developed larvae measure about two inches long.

A key way to differentiate forest tent caterpillars from other tent-making caterpillars is the location and appearance of the "nest" on the host plant. Forest tent caterpillars do not create a tent, but form a silk mat of larvae that group together on the trunk or tree branches. During the early period of their activity, these clusters are usually in the upper portion of the host tree, but as the population grows, clusters are more likely to be seen in the lower crown and on the tree's trunk. At times the cluster of caterpillar and number of larvae becomes so large that the webs cover the entire leafy crown of the tree.

BEHAVIOR, DIET & HABITS

Malacosoma disstria. Young larvae begin to feed on fresh, unfolding leaves until the next stage of development. The larva is the only of the four life stage (egg, larva, pupa and adult) that feeds on foliage. These insects overwinter as eggs; larvae emerge in the spring and feed for about two months; pupate in protected areas; and spend about a month as adults that mate, lay eggs and die.

Broadleaved hardwood trees such as sugar maples, oaks, birch, cherry, Aspen, Tupelo, cottonwood, elms, willow, ash, basswood and others are preferred hosts. Investigations suggest that red maples, sycamores and most species of coniferous trees are not fed upon.

Forest tent caterpillar infestations will cause twig and branches to die, but usually does not result in death of the tree. However, when recurring defoliation accompanies other factors that can weaken a tree's health – drought, growth in poor soils and late growing season complete defoliation – the result of the infestation may kill the tree.

REPRODUCTION

Mated female moths lay eggs in masses of 100 to 350 that encircle small twigs in the upper-crown region of a tree. Eggs are "glued" together by a foam-covered substance that hardens and becomes a glossy, dark-brown color.

SIGNS OF AN INFESTATION

The presence of forest tent caterpillar includes eggs, feeding larvae, adults and the clusters of silk seen on infested trees.

DISTRIBUTION

The forest tent caterpillar is native to the United States and inhabits hardwood forests and individual trees across the country.

OTHER INFORMATION

Your pest management professional can provide recommendations for managing problems caused by forest tent caterpillars. Some of these recommendations may include:

  • Protecting small, ornamental trees by collecting and destroying egg masses, destroying clusters of young larvae at the end of branches, or simply pruning away those areas of the tree that are supporting larvae.
  • Using insecticide products and microbial insecticides that are registered for control of forest tent caterpillars.
  • Doing nothing if the homeowner is not concerned with the appearance of the trees, since infested trees usually survive defoliation that occurs for only a few years.