Spring Cankerworm

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Pest Identification & Damage
Common Name(s): Spring Cankerworm, Spring Looper, Inchworm, Measuring Worm.

Scientific Name: Paleacrita vernata Peck. Order Lepidoptera. Family Geometridae. This insect attacks the foliage of a wide range of deciduous trees, including ash, hickory, red and white oaks, beeches, linden, maples, and hackberries, but it much prefers the leaves of apple trees and elms. There is one generation of this pest per year.

Identifying Characteristics for Damaging Stage(s): They are upon hatching green or brown worms which immediately begin to feed. They vary in color as they age, progressing from a light brown to black. This worm usually displays a subspiracular yellow stripe on each side. They are very dark ventrally. They have two pairs of prolegs near the ends of their larval abdomens. They grow to a length of between twenty and twenty-six millimeters. A distinct "looping" gait describes their manner of locomotion. Their backs arch up and the prolegs move close to the three pairs of thoracic legs. The anterior portion of the body then extends, after which the process is repeated. Another behavior is the way in which they will appear to rappel into space on a rapidly spun silken line when disturbed. They prefer to rest on twigs other than upon their feeding leaves.

Damage/Nature and Symptoms: Identification of Damage/Nature and Symptoms: Damage begins when small, ragged holes are chewed into the leaves. Once they are nearly mature larvae can skeletonize entire leaves. Small numbers of this pest are not injurious to large, healthy trees. Damaged leaves may give the tree a burned appearance. Also, with this species, there is an aesthetic devaluation that accompanies severe feeding damage with respect to ornamental plantings.

Distribution and Life Cycle Distribution: This insect is distributed from southeastern Canada southward into the Carolinas and west to south central Texas and northward into Manitoba.

Summary of Life Cycle: This insect overwinters as dark brown pupae twelve to thirteen millimeters long, four to five millimeters in thickness, embedded in the soil at depths ranging from twenty-five to a hundred or so millimeters. Generally, the nearer the tree base, the greater is the density of pupae.

Emergence occurs along a latitudinal gradient from February through April. The gray-brown males are strong fliers, active at dusk and during the early evening hours. Females are wingless and spiderlike in that they have very long legs. These females have a dorsal longitudinal black strip and a double row of dark red spines arched about the dorsum of each abdominal segment. They crawl up the tree trunks to find and mate with the males. Soon after mating, females deposit egg masses of varying sizes (up to fifty in a clutch) consisting of dark, oval-shaped eggs, placing them under bark scales and along hidden crevices. These hatch in about a month, and the larvae immediately begin to feed. They eat for three to four weeks, then drop via their silken lines and each digs out an earthen cell in which to pupate. They thus pass the remainder of the summer, fall, and the winter.

Management Methods:

Inspection/Survey Methods: Be aware of approximate local times when emergence is likely to occur and watch for signs. Sticky adhesives such as Tanglefoot are recommended for banding the lower trunks of trees in early spring, prior to emergence. Females attempting to crawl up are caught, and males attempting to mate may also be caught. Observe trees for caterpillars ("loopers") and evidence of leaf feeding when new leaves emerge in the spring.

Non-Chemical Management Strategies: To stop upward moving adult females, place sticky bands around tree trunks three quarters to one and a half meters above the ground. Place these prior to the first warm period in late winter or early spring, in our area as early as late February. Band all trees within about eighty meters of a tree which is known to be infested. These creatures are easily blown around by the wind. Soil may be very lightly tilled (to avoid root damage) near tree bases in order to expose pupae to the elements. This will also render them susceptible to bird predation. Horticultural oils may be used to great effect against eggs and early larval instars, since these stages are susceptible to suffocation. The larvae are susceptible to the Bt variant known as kurstaki which should be applied as a spray after the eggs hatch, but before the larvae are twenty-five millimeters long, when they are young and most susceptible.

Chemical Management Strategies: Chemical insecticides are also effective when they are timed to strike the early larvae. Local extension agents will help determine when all the eggs have hatched.

For the latest information on available chemical controls, consult the Pesticide Selection Guide. References:

Davidson, R. H., and W. F. Lyon (1989). Insect Pests of Farm, Garden, and Orchard (4th edition). John Wiley and Sons. New York et al.

Dress, B. M., and J. A. Jackson (1999). Field Guide to Texas Insects. Gulf Publishing Company. Houston.

Jackson, J. A. (1997). "Cankerworms." Bulletin L-1829. Texas Agricultural Extension Service. Texas A&M University.

Kemper Center for Home Gardening (2002). "Cankerworms.": MBG IPM at http://www.mobot.org/

Metcalf, C. L., et al (1962). Destructive and Useful Insects (4th edition). McGraw-Hill Book Company. New York et al.

Olkowski, W., et al. (1992). Common-Sense Pest Control (2nd edition). The Taunton Press. Newtown, CT.

Shetlar, D. J. (2000). "Spring and fall cankerworms." Fact Sheet HYG-2558-95. Ohio State University Extension.

USDA Forest Service (1989). "Insects and diseases of trees in the South." Protection Report R8-PR 16. USDA Forest Service Southern Region.