It’s tent caterpillar time again

StoryImage( ‘/Images/Story//img-T218fuVLAd.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘Tent caterpillars can devastate a tree’s foliage.’);

By early June, we should be observing a recurrence of tent caterpillars infesting our cherry, pear, maple, hawthorn, and many other types of trees. There are two species of tent caterpillars of importance to be found in the Rock River Valley—the more common Eastern tent caterpillar and the forest tent caterpillar.

The forest tent caterpillar is more common in the South and Southwest. The caterpillars of this species differ from that of the Eastern variety in that they have a row of keyhole shape spots down the back rather than a stripe.

We are made aware of the Eastern type’s presence when we notice an amorphous tent-like structure made of a silky material in a crotch of an infested tree. Closer inspection of the tent will reveal it is teeming with many small, black, and hairy caterpillars.

From the tent they have constructed, the worm-like creatures venture forth to feed on the leaves and buds of the tree on which they have set up housekeeping. The tent serves as a protective structure for the “worms,” and two or more batches of eggs may unite to form one large colony. During the heat of the day or rainy weather, the caterpillars remain within the tent. They emerge to feed in the early morning, evening, or at night if the temperature is not too low.

If the infestation of caterpillars is severe, the tree may be almost defoliated, and if it is small, or under stress for some reason, it may be killed. Providing the tree is healthy, it will usually be able to survive by growing new leaves. In the landscape, however, the tent nests can become an eyesore.

The caterpillars are actually the larvae of a smallish moth that is reddish brown in color with two white stripes running diagonally across each forewing. The adult moths emerge toward the end of summer, mate, and the female deposits eggs that will not hatch until the following spring.

About the middle of July, the caterpillars will have completed their growth, be about 2 to 2-1/2 inches long, and are ready to move into the pupal stage, the next step in their metamorphosis. Now they begin to wander away from their tent in search of a quiet, protected place to spin a silken cocoon in which to pass the pupal stage. Drastic changes in their anatomy transform them from a worm-like creature to an adult, flying moth during this resting and transformation stage.

The caterpillars can create a sizeable mess as they search out a suitable place to pupate. They may be seen crawling over other plants, walkways, driveways and even the sides of our houses, and they can create quite a nuisance when they are squashed. It is well to keep in mind, however, that at this stage they have done their damage to the trees for this particular year as their ravenous appetites have been satisfied, and they will not feed again.

A note for fishermen is in order. Tent caterpillars are excellent bait for bluegills, other sunfish, and an occasional bass, and I have had great luck using them. I affix one to a very small No. 10 or No. 12 size hook with a slipknot of thread. The hook is tied onto a small diameter leader of a floating fly line. By making a gentle cast with the fly rod, I am able to present the tempting morsel in such a way that it seems to be irresistible to members of the sunfish family.

The eastern tent caterpillar is difficult to control. Once the protective tent is completed, the commonly used garden insecticides cannot reach them. Small tents may be destroyed and removed by hand, and larger ones can be detached by pruning or by winding the nest on the end of a stick. I once had a neighbor who became so infuriated at the tent caterpillars infesting his pear trees that he attacked the tents with a propane torch. He got rid of the tents all right, but severely damaged some of his trees.

A preventive measure is to destroy the egg masses before they hatch in the spring. In late summer, the female moth deposits about 150 to 400 eggs in a mass that she covers with a shiny black, varnish like material. This egg case encircles a small branch and is about the size of a pencil in diameter. These masses are easily identified and can be readily removed and destroyed.

Nature helps in controlling tent caterpillars by providing natural predators and a few diseases. Small parasitic wasps of several families attack the caterpillars and lay eggs inside their bodies. The developing wasp larvae eventually devour the internal organs of the caterpillar. Birds enjoy feasting on tent caterpillars, and, aside from their use as bait for bluegills, I can think of no other benefit they offer the natural world. This does not mean, however, that their place in the web of life is not an important one.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

Enjoy The Rock River Times? Help spread the word!