A few weeks ago when forsythia’s bright yellow blossoms first appeared, tiny caterpillars hatched from dark Styrofoam-like egg masses attached to small branches of cherry trees and other trees in the rose family. Female moths deposited eggs last summer and their spawn marked time in the egg stage through autumn and winter. With the return of warm weather over the past weeks, dozens to more than 300 hundred larvae hatched from each egg mass. After hatching, hungry caterpillars move to buds and await the unfolding of tender young leaves. Caterpillars also 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, their tents enlarge and relocate to the crotches of branches near the center of the tree. Eastern tent caterpillars are a rather chummy lot and 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 body temperatures for more rapid growth and development during chilly spring days. After caterpillars have completed development, a mass exodus from the tree occurs and larvae wander the land seeking protected spots beneath logs, leaves, stones, or man-made structures to spin yellowish-white, silken cocoons. Adult moths emerge from cocoons. At this time, you may spot the tawny moths at your porch light. Adults mate and the female lays eggs on small branches of trees like a cherry or crabapple in your yard. These eggs house the next generation of caterpillars that will emerge with the bloom of forsythia next spring.
How do you know if you are likely to have a problem with eastern tent caterpillars? The best predictor of a problem this year is the problem you had last year. The images for this Bug of the Week came from a small stand of wild cherry trees perennially infested with eastern tent caterpillars. If you have a cherry, apple, or purple plum that was infested with tent caterpillars last spring, now is an excellent time to inspect carefully small branches and points where branches join the trunk of the tree. If tents are on small branches, a snip of the pruners can make short work of the problem. As the tents enlarge and move to the crotches of the tree, tents and their inhabitants are easily removed by hand, 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 flaming should not be used to remove these or any pest from a living plant. If left unchecked, 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 tree’s vigor. If you have a tall tree from which you cannot safely remove 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 tent caterpillars to innocuous levels. The last several years have been quite good for these rascals. We are keeping our fingers crossed in hope that Mother Nature will soon send a stimulus package to relieve us from these noisome creatures.
For more information on eastern tent caterpillars, visit the following web sites.