Forest Tent Caterpillars

a Forest Tent Caterpillar on a rosebush (Etna, ME; 6/4/2015)

Fully grown Forest Tent Caterpillars have keyhole-like, or shoe print-shaped, whitish spots on each body segment. This fine line of spots runs down the middle of the back for the entire length of the body. On each side there is a blue line, which gives them a bluish appearance. Their favorite hosts are oak, poplar, maple and birch but they can also be found feeding on the leaves of alder, basswood, cherry and willow.  The caterpillars do not build nests like the Eastern Tent Caterpillars do, but they do leave mats of silken threads on trees where they travel or rest.

In the past, Forest tent caterpillars have denuded forests in many areas in Maine for up to five years in a row. Trees can usually survive such defoliation, but with reduced growth.  Disease, other insects, nutrition, moisture and general poor condition may cause tree mortality in defoliated trees.  Higher defoliating populations of forest tent caterpillars typically drop after two years due to natural conditions and diseases.  Freezing weather shortly after eggs hatch kills large numbers of caterpillars, and excessively high temperatures later in the spring kills large numbers of adults and reduces the viability of newly laid eggs.

Additional Information: