Cankerworm

Facts, Identification, & Control

Scientific Name

  • Fall Cankerworm: Alsophila pometaria

  • Spring Cankerworm: Paleacrita vernata

Appearance

What Do They Look Like? Canker Worm Canker Worm image licensed under CC
  • Characteristics: Both species of cankerworm adults are very similar in appearance. Female adults are wingless, grayish-brown, and about 3/8 inch long. Male adults have wings.
  • Larvae: Larvae are about one inch long when fully grown. Fall cankerworm larvae range between light and dark green, while spring cankerworm larvae are brown or black.
  • Legs: Another way to differentiate between the two species is the number of legs on the rear half of the abdomen. Fall cankerworms boast three pairs of legs, whereas spring cankerworms possess only two pairs of legs.

How Did I Get Cankerworms?

Cankerworms, also known as inchworms, spanworms, loopers, or measuring worms, are a common outdoor pest. Infestations come in cycles, and periods of high population last around four years. Certain types of trees draw these pests, and porch lights may also attract flying adults.

How Serious Are Cankerworms

Large numbers of the insects can defoliate a tree, leading to extensive damage if they persist for several seasons. During years of peak activity, homeowners have higher chances of finding them eating tree leaves and crawling up the outside of homes and other buildings.

Cankerworm larvae can also make spending time in the yard unpleasant. These caterpillar-like pests drop down from tree branches on silken strings, often ending up on people, picnic tables, and walkways.

How Do I Get Rid of Cankerworms?

What You Can Do

A non-chemical, but limited cankerworm control option available to homeowners is to place a band of sticky adhesive on the host tree trunk. The sticky substance captures the wingless female adults as they crawl up the tree trunk and before they have the chance to lay eggs.

However, the properly timed use of insecticides is more effective if the application coincides with the presence of young larvae that are just beginning to feed on the host tree leaves. It always is a good idea to get your pest management professional’s advice and recommendations in order to maximize the chances for effective insecticide use for cankerworm control.

What Orkin Does

Your local Orkin technician is trained to help manage cankerworms and similar pests. Since every building or home is different, your Orkin technician will design a unique program for your situation.

Orkin can provide the right solution to keep cankerworms in their place…out of your home, or business.


Behavior, Diet, & Habits

What Do They Eat?

Spring and fall varieties of cankerworm larvae feed at the same time of the year, regularly on the same trees, and cause similar damage. As the larvae feed on leaves, they create tiny holes resembling the size and shape of BB's on the leaves. As the larvae become larger, feeding continues until the only leaf tissue remaining is the leaf veins.

Cankerworms are defoliating pests of many hardwood tree species, but their preferred host trees are:

  • Ash
  • Basswood
  • Beech
  • Black cherry
  • Maple
  • Oak

Life Cycle

Spring and fall cankerworm are long-standing forest and shade-tree pests of forests. The common name of each species comes from the time of year when the adult moths appear, not when the larvae are present. Both complete their life cycle by developing in four distinct phases:

  1. Egg
  2. Larvae (Caterpillar)
  3. Pupae (Cocoon)
  4. Adult
Pupal Stage

By mid-summer, the larvae of both species begin dropping to the ground from the host tree using a silk thread they produce. Once on the ground, they burrow into the soil, spin a cocoon, and pupate. Fall cankerworm pupae remain in the soil until they develop into adults in the late fall. Spring cankerworms also pupate in the soil, but do not emerge as adults until the early spring of the subsequent year.

Reproduction

Mating occurs as the emergent females crawl up tree trunks to lay eggs. Both cankerworm species have their egg hatch at about the same time in the spring. Each species normally completes one generation per year in most areas.