Leafcutter infestations have been recorded since the late 19th century. Once a major outbreak begins, defoliation can occur annually for 6 to 8 years. During an extensive outbreak in eastern Ontario in 1981, maple was defoliated throughout 321,000 acres (130,000 ha). In Vermont during the mid-1970s, trees on more than 35,000 acres (14,000 ha) were heavily defoliated. Studies in Vermont indicated that 3 years of complete defoliation by this insect were required to significantly reduce the starch content of maple roots (an indication of physiological stress). Several consecutive years of defoliation may result in crown dieback, though there usually is little mortality, even when trees are defoliated heavily for as many as 7 years. Sugar maple apparently is more resilient to defoliation by the leafcutter than to that of other insects, probably because of its unique feeding behavior and late-season feeding. Repeated, heavy defoliation significantly reduces sap production.

The moths are steel blue with bright orange heads but they are small and rarely noticed. This insect is most readily detected by the appearance of infested foliage. During mid- to late June, caterpillars mine the leaves, creating brown blotches 0.5 to 0.8 inch (12 to 20 mm) long (Fig. 37). Leaf mining stops after 2 to 3 weeks when the caterpillars begin to skeletonize foliage as they feed from a protective circular case that is constructed from two discs of leaf tissue (Fig. 38). The case is portable and must be replaced as the caterpillar grows. Each time a circular disc is “cut” from a leaf, a hole is created. Frequently, a major leaf vein is severed. The end result is foliage that contains several holes. The larges are about 0.75 inch (2.0cm) in diameter. The leaf is brown and partially skeletonized but otherwise intact. When feeding is completed in late August or early September, caterpillars descend trees, bringing their cases with them. Observant sugarbush operators often see a bizarre sight of hundreds of pieces of brown foliage walking down tree trunks and across the ground!