Eastern Tent Caterpillar

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Easter tent caterpillars looking for a place to spin their cocoons and pupate

Eastern tent caterpillars looking for a place to spin their cocoons and pupate. Photo by J. R. Baker

Eastern Tent Caterpillars hatch about the same time as our native tree the Eastern Redbud starts to bloom. This insect overwinters in egg masses attached to the twigs of host trees, with wild cherry being one of its favorites. The caterpillars hatch in spring when the new leaves are opening on the trees.

After a few days of feeding, the caterpillars begin to weave communal tents in the crotches of trees, enlarging the tents as they grow. In large numbers they can defoliate a large portion of a tree or even the entire tree. This can weaken the tree, but rarely kills it.

The caterpillars will feed for about six weeks, then will leave the host tree in search of a place to pupate. The mature caterpillars are easy to identify:  they are about 2” inches long, black and slightly hairy with a pale-yellow stripe down the back that has a row of clear blue spots along each side. They like tree trunks, fences, or your patio furniture. You may see silky, off-white colored cocoons stuck in the mortar between the bricks on your house. If you have large numbers of these caterpillars it can be very annoying when they are crawling all over the place. Thankfully this only lasts a few days!

The adult moths will hatch from the cocoons after a few weeks. They emerge at night, so often go unnoticed. The adults fly back to the trees, where they mate and the female lays eggs for the following year. The eggs masses are attached to and encircle small twigs, and are black and somewhat shiny.

What’s the best method to control these pests? As soon as you see the small tents, go out late in the evening or on a rainy day, tear them out and discard them in a bucket of liquid dish washing solution. If the nests cannot be safely reached from the ground, you can use an organic control called Bt. Bt is short for Bacillus thuringiensis, a biological pesticide that contains a bacterium that will kill young, leaf eating caterpillars without killing other beneficial insects or honey bees. You must spray the leaves of the plant as the insecticide must be ingested. Spray when the caterpillars are small because they become increasingly tolerant to insecticides as they mature. Always read and follow the label directions when using any pesticide.