Forest tent caterpillar

The forest tent caterpillar (Malacosoma disstria) is a moth of the Lasiocampidae family. Despite its common name, this species does not actually construct a tent-like silk nest, unlike other members of the genus. Instead, they form communal silken mats on the trunks or branches of host trees, which serve as gathering points for molting and resting.

The host range is broad, focusing primarily on deciduous trees such as aspen, oak, birch, sugar maple, and poplar. During peak outbreak years, these insects can cause extensive defoliation, covering vast forest tracts. This process stresses the trees significantly, making them more susceptible to subsequent attacks by secondary pests and various fungal pathogens.

The life cycle begins with eggs, which are deposited in masses circling the small twigs of host trees. They remain in the egg stage throughout the winter. Upon spring bud-break, larvae hatch and begin feeding immediately. The larval stage consists of several instars, followed by pupation, where larvae spin protective cocoons within rolled or folded leaves, eventually emerging as adult moths.

Feeding behavior is highly destructive. Young larvae skeletonize the leaf surface, while mature larvae consume the entire leaf lamina, leaving only the midribs and petioles intact. A single major outbreak can render a stand of trees completely bare within weeks, resulting in significant growth loss and, if repeated for three or more consecutive years, widespread tree mortality.

Integrated Pest Management (IPM) is the standard approach to mitigation. Preventive measures include monitoring egg mass density during dormant winter months. In managed forests or urban settings, direct control is achieved through the aerial or ground application of biological insecticides containing Bacillus thuringiensis, which specifically targets the caterpillars while sparing beneficial insect species.