Forest tent caterpillars (Malacosoma disstria), found on broadleaved trees, range throughout the United States and Canada. Young larvae appear when the leaves are beginning to unfold. Colonies stay together and move about in a file, following silk trails laid down by leaders. The caterpillars do not spin a tent; instead, they form a mat on the trunk or branch, and here they congregate when at rest or during molting periods. They also spin silk strings which act as parachutes, that they use to move up and down from the crowns of trees. Ludlow, Massachusetts, in summer.