Gypsy Moth: Know the Facts

Gypsy moth is a name we hear more and more in some parts of northern Illinois. Unfortunately, we’re not always hearing all the facts that we should. This article will describe the pest in its various life stages, so homeowners can know if they have this pest or something else. Damage and preventative measures will also be outlined here.

Life Cycle and Description

The moth (the adult stage) is usually present in July and August. The male moths are brown and tend to fly in zigzag patterns. The female moths are white or cream colored and do not fly at all. The female lays her eggs in masses, usually on branches and trunks of trees. Egg masses can also be found on patio furniture, recreational vehicles and other outdoor items. The egg masses are cream or buff in color and about an inch or so in length. They are present from July or August until the following May.

The caterpillars hatch out of the eggs around the time when many hardwood trees are starting to leaf out (usually around May). The caterpillars enlarge as they go through 5 or 6 growth stages (called instars). Younger caterpillars are usually feeding in the top of the tree and may go unnoticed on large trees. Older caterpillars may move up and down the tree. Older caterpillars are very distinct in their appearance. Long hairs protrude from the caterpillar’s body and rows of colored "bumps" can be seen on the caterpillar’s back. There are four pair of blue "bumps" followed by six pair of red "bumps". Feeding by the caterpillars occurs in May and June.

The caterpillars mature in late June and early July, then enter a pupal stage. During this time the caterpillars are turning into adult moths. Pupae are dark and do not move. Pupae can be found under bark, in crevices, in sheltered areas and even on the ground. The insect remains in the pupal stage for 7-14 days and then emerges from its pupal case as an adult moth.

Host Trees and Damage

Gypsy moth caterpillars prefer hardwood trees and will feed on many different species (including, but not limited to oak, apple, some poplars, willow, alder and hawthorn). The caterpillars are defoliators; they eat the leaves of the host trees. Young caterpillars eat small holes in the middle of the leaves, while older caterpillars feed from the outer edge of the leaf inward.

What to Do?

If you suspect your tree has gypsy moth, contact your local University of Illinois Extension office for help in correctly identifying the pest. Gypsy moth is often confused with other leaf feeding caterpillars. If it is confirmed that you have gypsy moth on your property, you should call the local office of the Illinois Department of Agriculture. They are the lead agency in mapping the movement of this pest and trying to slow its spread in Illinois. If you find egg masses on trees or outdoor equipment, you can scrape them off and destroy them. Treating the caterpillars with insecticides can be difficult for the homeowner, since caterpillars most often feed high in the top of the tree. Treating may make it more difficult for the Department of Agriculture to monitor the pest. Contact the local office of the Illinois Department of Agriculture before attempting any treatment.

August - September 2000: Gypsy Moth: Know the Facts | Flood Tolerant Trees | Saving Seed from the Garden | Ideal Time for Lawn Renovation