Lambdina fiscellaria and Lambdina athasaria

Two species of geometrid (inchworm; looper) caterpillars are collectively referred to as the hemlock looper. Lambdina fiscellaria and L. athasaria are common native defoliators of hemlock that are found in Canada and the United States. (Additional subspecies may also occur.) Both may be found in mixed populations on their hosts. They are most significant as pests of hemlock and balsam fir, but have also been reported from larch, spruce, and arborvitae. Hemlock loopers have a black band with white teardrop-shaped spots along the length of the body. Tiny eggs (1 mm.) overwinter and hatch in late May or early June, and the young larvae begin to feed on the foliage of their host plants. Young larvae prefer new foliage, however as they age they will feed on old needles from other conifers. (Additional deciduous hosts have also been reported, such as sugar maple and white birch.) Hemlock loopers are described as wasteful feeders, not consuming the entire needle. Larvae grow slowly, and complete their maturation by late August or early September. Four or five instars are reported, depending upon the location. Mature hemlock loopers are approximately 1.18 inches in length. Caterpillars drop to the ground to pupate by late July. Pupae are generally brown and green with dark spots and not found within a cocoon. Adults emerge by September and October. Moths are small (approx. 1.25 inch wingspan) and tan to gray/brown in color. When populations are high, large numbers of these moths may be found mating and resting at the base of trees or surrounding vegetation. Eggs are laid singly on the bark of the trunks and limbs of trees at that time (Johnson and Lyon, 1991). Historically, populations may be heavy for 2 to 3 years, then virtually disappear (Robert Childs, Personal Communication). Outbreaks may be difficult to predict. (The University of Maine Cooperative Extension provides great information about historical outbreaks of these insects in Maine and Newfoundland.)