Dispersing eastern tent caterpillars (ETC) can pose several problems as they leave their “home” trees (commonly, wild cherry) over the next 10 days, or so.
The greatest potential harm is associated with pregnant mares on pasture. Ingestion of these hairy caterpillars (Figure 1) triggered early and late term foal abortions associated with Mare Reproductive Loss Syndrome (MRLS). Keep pregnant mares away from ETC-infested fencerows until caterpillar movement has subsided.
In addition, these hairy caterpillars pose a significant nuisance to landscapes located near concentrations of the caterpillars on wild cherry trees, their favored host. Wandering larvae may move several hundred yards, using the sun as a compass to direct their general movement. They tend to move in the morning or afternoon; those abandoning trees in the afternoon tend to move the farthest. ETCs orient themselves to contrasting vertical objects, so they may climb fence posts or structures encountered during their journey.
The large size and hairy covering of the caterpillars tends to limit the effectiveness of insecticides, so chemical control is often unsatisfactory. Direct sprays of landscape insecticides containing a pyrethroid (bifenthrin, cyfluthrin, cyhalothrin, or permethrin) or carbaryl (Sevin) are among the best choices. Insecticidal soap is also an alternative. The results of these applications are slow to appear, so they can seem to be completely ineffective.
When practical, sweep up caterpillars and dump them into a trash bag, and then seal it. The Velcro-like hooks on the fleshy abdominal legs causes them to cling to rough surfaces, which often turns removal efforts messy.
The wandering stage of the ETC life cycle lasts several days. Ultimately, the wanderlust will pass and the caterpillars will find sheltered places to spin cocoons and pupate. Adults will be active during June, laying eggs for next year’s generation.
By Lee Townsend, Extension Entomologist