The spring cankerworm is a native pest to the deciduous forest and ornamental trees of North America, including Apple, Ash, Cherry, Elm, Honeylocust, Linden, Maple, Red and White Oak, and many more trees and shrubs.
Common throughout most of North America.
- The common name of each species comes from the time of year when the adult moths appear, not when the larvae are present.
- Cankerworms, also called inchworms or loopers, are caterpillars that move with a distinctive “looping” motion. Small numbers of cankerworms are usually present most years, but outbreaks can occur and cause significant defoliation of a variety of trees.
- This species of moths have slender, dull grey-brown bodies and large, broad forewings. Males are about one inch long, while wingless females are about a quarter-inch long.
- Spring cankerworm eggs are laid in smaller clusters. Individual eggs are silvery-beige in color and spindle-shaped.
- Spring cankerworm larval color ranges from greenish-yellow to yellow-brown to black. They have one larger stripe down either side of their bodies.
- They are about an inch long when fully grown. Cankerworms have a distinctive appearance and movement as they have fewer legs along their abdomen than typical caterpillars. Most cankerworms have five pairs of abdominal legs, while the spring cankerworm has two pairs.
- Spring cankerworms complete their life cycle in four distinct phases: egg, larvae, pupae, and adult.
- They overwinter as pupae and emerge as moths in February/March. The females crawl up tree trunks, are mated, then lay eggs in masses under loose tree bark.
- Eggs hatch in early spring, and females of both species lay approximately 50 eggs. Larvae feed on foliage for 3 to 6 weeks, then crawl down the trunk or drop by silk threads to the ground. Once on the ground, they burrow into the soil, spin a cocoon and pupate.
- Spring cankerworm moths emerge in early spring.
- Cankerworms have one generation per year.
Damage and Detection
- Newly hatched larvae eat the young leaves as well as the buds of numerous deciduous trees, including apple trees.
- Larger larvae eat all but the midribs or tougher veins of mature leaves.
- Most damage occurs about the time the leaves become fully developed and can include tattered leaves with random holes and fully chewed areas of foliage.
- In an infestation, trees may be completely stripped of foliage. Death is likely if the trees have been defoliated more than once or are in a weakened state.
Prevention and Control
Cankerworm females need to climb up tree trunks to lay their eggs. Barriers in the form of a band of sticky adhesive 5-6″ wide around tree trunks can capture the female adults as they make their way up to lay eggs.
- Although the use of insecticides for cankerworms is discouraged, recurring defoliation can be severely damaging to trees and may warrant application.
- To treat larvae, an effective organic option is a product containing Bt (Bacillus thuringiensis). It must be applied while larvae are still less than 1/2-inch long.
While every effort has been made to describe these plants accurately, please keep in mind that height, bloom time, and color may differ in various climates. The description of these plants has been written based on numerous outside resources.