Appearance

Adult moths are brown to tan in color. Their front wings have two white or yellowish lines that extend from one side of the wing to the other. The adult’s wingspan is about 1-¼ to nearly two inches wide. The female moth lays eggs in upright rows about the diameter of a pencil on twigs. The amassed eggs often encircle the twig. The female discharges a frothy substance that, when dried, gives the egg mass the appearance of being shiny and black.

Full grown larvae are about 2-½ inches long, black, hairy, with a white stripe down the back, brown and yellow lines along the sides and a row of oval blue spots on each side.

While forest tent caterpillar webs are sometimes mistaken for eastern tent caterpillar webs, there are some important differences between these two insects. Fall webworm webs are located at the ends of branches and completely surround plant foliage. Eastern tent caterpillar webs are built in the crotch and the forks of the host plant’s limbs. Also, the eastern tent caterpillar begins building webs earlier in the growing season than forest tent caterpillars and is among the first insects to come out of their overwintering sites and become active in the early spring.

Behavior

Malacosoma americanum overwinters as an egg mass, and it hatches in early spring. After hatching to become larvae, they begin building their web tent and feed for about six to eight weeks. Once the larvae have completely matured, they move to protected areas and spin their individual cocoon. Larvae do not feed within their webs; instead, they move away from the web, feed elsewhere on the host and return back to the web for protection. Larvae feed three times per day – just before dawn, after sunset and sometime near the middle of the afternoon. In their final phase as caterpillars and just before becoming pupae (cocoons), larvae change their feeding pattern and feed only at night.

Preferred hosts are cherry, apple and crabapple trees, but this insect may infest hardwood trees such as ash, birch, oak, maple and poplar. Also, eastern tent caterpillar larva often infests ornamental shrubs and trees. While eastern tent caterpillar webs impact the appearance of landscaping trees, infestations rarely cause tree mortality.

Reproduction

Mating and egg laying usually occurs the same day that moths emerge from their cocoons. An egg mass laid by the female moth contains about 150-400 eggs.

Signs of Infestation

Their web “tents” built in the forks and crotches of trees notes the presence of eastern tent caterpillars.

Distribution

Eastern tent caterpillars are found throughout the eastern United States and extend westward to the Rocky Mountains and northerly into southern Canada. These insects are native to the United States and are not an invasive species.