Forest Tent Caterpillar Moth

Mature (pre-pupating) larvae are 2 to 2.5 inches (50 to 64 mm) in length. The caterpillars are black, dark brown, or gray, with broad blue longitudinal stripes and thin yellow stripes extending along each side. The back of each abdominal segment bears a white spot that is wider toward the head end. The sides are partially covered with fur-like long setae. The adult moth that emerges after pupation is yellow or tan with a thick, short, furry body. The wingspan is about 1.5 inches (30 mm). Coloration is similar for males and females. The female's body is larger than the male's. The insect is native to North America.

Forest tent caterpillar populations increase periodically to outbreak densities. Not much is known about the factors that lead to the initiation of forest tent caterpillar outbreaks, although some plausible mechanisms are higher temperatures in the spring, phenological synchrony with their host plants, and reduced predation enemies. Whatever the cause, outbreak densities give rise to cyclic population dynamics, characterized by highest fecundity at peak population density and reduced fecundity for several generations during decline. At low population densities, moths are found mating high above the ground, in the forest canopy. Mating starts late in the day and copulations are short. In contrast, during high-density outbreaks, mating takes place on lower vegetation, presumably because caterpillars descend to forage in less defoliated areas, where they form their pupae. This high population density increases the operational sex ratio and significantly intensifies male-male competition. As a result, copulations begin earlier in the day and last longer in an attempt to minimize sperm competition. In addition, such high densities enhance female opportunities for being selective regarding males. During high outbreak densities, some males, called "hangers", change their copulation behavior. …