Forest Pests: Insects, Diseases & Other Damage Agents

Lepidoptera: Geometridae

Hosts: Maple, oak, linden, beech, apple, birch, elm, hickory and other hardwoods

Evidence: In the spring, look for larvae that move in typical inchworm fashion. Linden loopers are dull-to-brightly yellow-sided (a). Bruce spanworm larvae are variable in color, ranging from vivid green to dark brown, with three thin yellow lines on each side of the body (b). Spiny loopers are pinkish with hairy tubercles and black lines running their length (c), and fall cankerworm larvae range from very light green to dark brownish-green. The head and anal segments are also variable in color, ranging from pale green to black or mottled. Darker larvae may have a longitudinal black stripe, while lighter color forms have white lines running their length (d). Though larger loopers tend to feed voraciously, consuming all but the mid rib and larger veins, younger larvae may work as skeletonizers (eg., fall cankerworm) or give leaves the appearance of Swiss cheese (eg., Bruce spanworm).

Life Cycles: Each of these loopers has one generation per year. Winter is spent in the egg stage, with the exception of the spiny looper, which overwinters as a pupa beneath litter. The adult female moths of all four loopers are wingless, and, with the exception of the spiny looper, moths are active into the fall, when females may be seen crawling up the base of trunks. With the spiny looper, adults emerge and mate in the spring.

Management: These species of loopers are often found in association with each other. Parasites and disease are credited with keeping them in check, though periodic epidemics occur. Urban trees appear to be especially susceptible to heavy feeding by some species of loopers. Sticky bands around tree trunks will protect isolated trees by preventing females from crawling up to lay eggs. Insecticides, including Bacillus thuringiensis, are effective once larvae begin to feed on leaves.