While forsythia’s bright yellow blossoms are the harbinger of spring, they also mark the emergence of an impressive tree pest, the eastern tent caterpillar. Last summer, autumn, and winter these rascals marked-times as eggs on the small branches of trees like cherry and apple. With a few warm days in the last week, tiny caterpillars are beginning to hatch from the dark brown, Styrofoam-like egg masses. More than 300 hundred larvae can be found in a single egg mass. After hatching, caterpillars move to buds and await the unfolding of tender young leaves. Larvae build small silken tents over buds and the surrounding branch. From this bivouac they move along silken trails to expanding leaves and munch nutritious foliage. As larvae grow during March and April, they need more space to hide and develop and they enlarge their tents. Eventually, tents will be constructed in the crotches of large branches or where limbs diverge from the trunk.
Eastern tent caterpillars are a rather chummy lot. Brothers and sisters from the same egg mass often participate in group activities such as communal foraging and enlarging their remarkable tent. This silken home provides protection from predatory and parasitic insects. Tents may also help caterpillars conserve moisture and elevate their body temperature for more rapid growth and development during chilly spring days. These hairy caterpillars have voracious appetites. They strip even large trees of leaves when many tents are present. After caterpillars have completed development, a mass exodus occurs from the tree and larvae wander the land seeking protected spots beneath logs, leaves, stones, or man-made structures to spin yellowish-white, silken cocoons. The adult eastern tent caterpillars emerge from cocoons as moths in June or July, mate and lay eggs on small branches of rosaceous trees such as cherry, apple, and crab apple. These eggs house the next generation of caterpillars that will emerge with the bloom of forsythia next spring. How do you know if eastern tent caterpillars threaten your trees? The best predictor of a problem this year may be the problem you had last year. The images of this bug of the week came from a small stand of wild cherry trees that are perennially infested with eastern tent caterpillars.
If you had a cherry, apple, or purple plum with tent caterpillars last spring, now is an excellent time to carefully inspect the pencil sized branches for egg masses and tiny silken webs. The egg masses are easily removed with a pinch of the fingers or if you are a bit squeamish about touching bugs, simply get out your nippers and prune them out. As the tents enlarge and move to the crotches of the tree, tents and their inhabitants can be removed with a gloved hand on a cool day, placed in a bag, and destroyed. The old school remedy of “burning them out”, though dramatic, went out with the storming of Frankenstein’s castle. Flames are very damaging to the bark of a tree and should not be used. Tall trees festooned with tents may be totally stripped of leaves. While trees may recover and produce a second flush of leaves, repeated defoliation reduces the vigor of trees. If you have a tall tree from which you cannot safely remove eggs or tents, you may want to seek the help of a professional certified arborist. Entomologists believe that eastern tent caterpillar populations run in cycles. After a few years of caterpillar plague, natural enemies such as predators, parasites, and pathogens reduce the tent caterpillars to innocuous levels. Last year was a very good year for eastern tent caterpillar and a quick inspection round and about our campus indicates trees are again about to be festooned with tents.
For more information on eastern tent caterpillars, visit the following web sites.