The forest tent caterpillar (Malacosoma disstria) is a native North American insect known as a major defoliator. Its larvae consume the leaves of various broadleaf trees. Understanding its diet is necessary for comprehending its impact on forested and urban environments. The caterpillar’s food preferences range from highly favored species that sustain large populations to secondary hosts consumed only out of necessity.
Primary Host Trees
The diet of the forest tent caterpillar centers on select hardwood species that provide optimal nutrition for larval growth and survival. These primary host trees are where outbreaks typically originate and are sustained. In boreal forests, the trembling aspen (Populus tremuloides) is the most commonly preferred food source, offering the necessary leaf chemistry to support large, healthy caterpillar populations.
Other highly favored species include various poplars, birches (Betula spp.), oaks (Quercus spp.), and maples (like sugar maple). They also readily feed on ash (Fraxinus spp.) and basswood (Tilia spp.) in temperate regions. The availability and foliage quality of these preferred hosts allow the caterpillars to complete their larval development efficiently.
Dietary Flexibility and Secondary Food
Although the caterpillar prefers certain trees, it exhibits high dietary flexibility when primary food sources become depleted. During outbreaks, intense competition forces the caterpillars to wander widely, leading them to consume the leaves of numerous less-preferred hardwoods and shrubs.
Secondary hosts include fruit trees (apple and cherry), willow, and sweetgum. If the forest canopy is stripped bare, the larvae may turn to atypical hosts like vegetable crops, roses, or azaleas. These secondary foods are lower quality, and caterpillars feeding solely on them may experience reduced growth rates or fail to complete development. One notable exception is the red maple (Acer rubrum), which contains chemical compounds that deter feeding.
Feeding Patterns and Impact
The feeding behavior is highly synchronized, beginning in the spring shortly after the eggs hatch and host tree leaves expand. The young caterpillars are gregarious, feeding together in groups on the emerging foliage. They spend the next five to six weeks growing, with the final larval instars being the most voracious feeders.
During this period, the caterpillars consume entire leaves, a feeding style that leads to complete defoliation rather than the skeletonizing seen in some other species. The immediate consequence is the rapid stripping of foliage, which causes significant stress by forcing the tree to expend stored energy reserves to produce a second flush of leaves.
The caterpillars lay down silk trails as they move to and from their resting mats on the tree trunk. Although healthy trees typically produce new leaves within weeks of the defoliation event, the immediate impact is a reduction in growth for that season. Repeated years of complete defoliation can weaken a tree, making it more susceptible to other environmental stressors.