Gypsy moth, eastern tent caterpillar, forest tent caterpillar and cankerworms

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

In our conference call on Wednesday, June 11, several agents had observed incorrect diagnosis of caterpillars at garden centers and other places. Usually what happened was that a homeowner brought in an eastern tent caterpillar or forest tent caterpillar and was told that it was a gypsy moth caterpillar. It is not difficult to distinguish these four caterpillars that are abundant this time of year. People are finding eastern tent caterpillar and forest tent caterpillars wandering everywhere now because they have finished feeding and are looking for a nice protected site to pupate. Spring and fall cankerworms still have another week or two to feed (in Lansing) before they pupate, and gypsy moth caterpillars won’t be done feeding until late June or early July.

Mature gypsy moth caterpillar
Mature gypsy moth caterpillar.
Photo credit: J. Appleby, Univ. of Illinois ©

The eastern tent caterpillar is easily distinguished from the other three because it is the only caterpillar to make a silk nest in the crotch of small trees or where several limbs meet on larger trees. If you discover a wandering caterpillar, both the eastern and forest tent caterpillars have thick, tan hair and are dark in color with irregular blue and white mottling. Some of the white markings define stripes. The eastern tent caterpillar has a diagnostic solid white stripe down the back, while the forest tent caterpillar has a series of keyhole-shaped spots.

The gypsy moth caterpillars are also hairy, but lack the white stripe down the back or the series of keyhole-shaped spots found on the tent caterpillars. Instead, gypsy moth caterpillars have three pairs (one pair per segment) of large blue tubercles on their back just behind the head followed by many pairs of red tubercles. The blue and red tubercles are easy to see on large (two-inch long) caterpillars, but are more difficult to see on smaller caterpillars which tend to be much darker in color.

The spring and fall cankerworms can be distinguished from the other three by their missing prolegs and “looping” behavior. They loop when they crawl and are often referred to as loopers or inch-worms because of this. A closer examination will reveal that they have only two or three pairs of fleshy prolegs instead of the standard complement of five pairs of prolegs.

Eastern tent caterpillar
Eastern tent caterpillar.

Eastern tent caterpillar larva
Eastern tent caterpillar larva.

Forest tent caterpillar
Forest tent caterpillar.

Eastern and forest tent larvae
Eastern and forest tent larvae.

Fall cankerworm
Fall cankerworm.

Gypsy moth larva.
Gypsy moth larva. Photo credit:
Cooperative Extension University of California

Dr. Smitley’s work is funded in part by MSU‘s AgBioResearch.

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