Eastern tent caterpillars (ETC) are easy to spot now in wild cherry and related trees. Most tents on limbs now range from softball- to football-size. As the caterpillars grow, they will begin to leave the small tents on limbs to form fewer, larger tents at branch angles along the trunk. Tent caterpillar development is not synchronized so it is common to find small and large individuals in the same tents and limb and trunk tents on the same tree.
ETC will feed for 4 to 6 weeks; full-grown larvae will be 2 to 2 ½ inches long. These mature larvae are restless and soon leave their host trees. After crawling as far as several hundred yards, they will settle in a protected site, spin a cocoon, and pupate. Moths will emerge in June and females will lay eggs for next year’s generation.
Hundreds of these wandering caterpillars can pose significant problems:
1) Ingestion of large numbers by pregnant mares during the spring of 2001 resulted in early fetal loss and late-term abortions in more than 3,000 mares (Mare Reproductive Loss Syndrome). With ETC populations apparently increasing over the past few years and the possible regrowth of wild cherry along fencerows, it is important to assess ETC populations near pastures with pregnant mares. Preventive steps should be taken while caterpillars are still feeding in infested trees. Move mares to pastures where the risk of ETC exposure is minimal, if practical. If mares cannot be moved, then destroy or remove tents while the caterpillars are present or treat around active tents with appropriate insecticides. ETC usually are in their tents during the day. Take advantage of this behavior.
2) Hundreds of wandering ETC caterpillars can overrun yards, patios, and houses. They are not harmful but can be a significant nuisance. Because of the differences in development, crawling caterpillars can be around for several weeks, so the annoyance lingers. While direct sprays with labeled insecticides may give some control, usually the percentage kill is relatively low and the action is not very quick. The key is to deal with ETC while they are still feeding in infested trees (see above).
The ETC population collapsed shortly after the 2001 outbreak due to actions of predators, parasitoids, pathogens, and weather factors. However, natural recovery follows and numbers begin to grow. ETC cycles tend to last 9 to 12 years so it is time to anticipate an upswing.
By Lee Townsend, Extension Entomologist