It is likely eastern tent caterpillars (ETCs) will begin to hatch soon, according to Lee Townsend, University of Kentucky College of Agriculture, Food & Environment extension entomologist.

According to Townsend, after spending about nine months as eggs in masses on twigs of wild cherry and related trees, the first few tiny ETCs of the season soon should be leaving their eggs.

“The onset of the single generation that occurs each year varies with the character of the season. Hatch was noted as early as March 14, 2012, during an unseasonably warm spring, and as late as April 2, 2014, during one that was slow to develop,” he said.

The larvae are among the first insects to become active in the spring and are prepared to cope with Kentucky’s erratic temperature swings.

“Egg hatch is relatively random and occurs over an extended period. This increases the chance for survival in case of late freezes,” Townsend said. “In addition, the small but hardy caterpillars will remain clustered on egg masses to ‘wait out’ temperatures that are too low for feeding and development. ETCs grow and develop when the temperature is above 37°F.”

When mature, the 2 in.- to 2.5 in.-long hairy caterpillars wander from their developmental sites along fence lines.

Consumption of large numbers of caterpillars by pregnant mares precipitated staggering foal losses in the mare reproductive loss syndrome outbreak of 1999-2001. The syndrome can cause late-term foal losses, early- and late-term fetal losses and weak foals.

University of Kentucky researchers conducted studies that revealed that horses often inadvertently eat the caterpillars, and the caterpillar hairs become embedded in the lining of the horse’s alimentary tract. Once that protective barrier is breached, normal alimentary tract bacteria may gain access to and reproduce in sites with reduced immunity, such as the fetus and placenta.

If practical, farm managers should plan to move pregnant mares from areas where wild cherry trees are abundant to minimize the chance of caterpillar exposure, the university said. The threat is greatest when the mature tent caterpillars leave trees and wander to find places to pupate and transform to the moth stage.

ETCs are also a significant nuisance to people living near heavily infested trees, as the caterpillars may wander hundreds of yards in search of protected sites to spin cocoons and pupate.

According to Townsend, while it is possible to predict approximately when to expect tent caterpillar activity, there is no reliable information to track general population trends other than observing local activity and watching for tents to develop from mid-March through mid-April.

To get rid of active caterpillars, Townsend recommends pruning them out and destroying the nests, if practical. Farm managers can use any one of several biorational insecticides registered for use on shade trees, as needed.