Instead, they spin pad-like structures on trunks and on branches where they go to rest and to moult. Other aspects of the forest tent caterpillar are similar to those of the eastern tent caterpillar. They may be ugly and unsightly but their defoliation rarely kills host trees unless these trees are already diseased or under stress due to climatic or other environmental factors. Forest tent caterpillars have a brownish body with bluish lines along the side. With each moult, a line of white, footprint-shaped spots becomes visible.
Moths are yellowish-brown and chunky with two dark lines on the forewings.
Forest tent caterpillars start their lives as eggs laid in shiny brown bands of 100 to 300 around twigs. Caterpillars emerge as new leaves begin to appear and begin feeding and constructing their nests immediately. During the five or six weeks of the caterpillar stage, they go through four moults. After the last moult, the caterpillars spin yellowish cocoons in some sheltered place in which the final transformation to moth takes place. Moths emerge from the cocoons after about 10 days to mate, lay eggs and then die.