Eastern Tent Caterpillar Hatch Underway Soon in Central Kentucky

Eastern tent caterpillars, which can cause fetal and foal losses, should start hatching soon in Kentucky.

Eastern tent caterpillar egg mass on wild cherry twig. Courtesy Dr. Lee Townsend

It is likely that Eastern tent caterpillars (ETC) soon will begin to hatch, according to Lee Townsend, PhD, University of Kentucky College of Agriculture, Food and 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 eastern tent caterpillars 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 they 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. ETC grow and develop when the temperature is above 37 degrees F.”

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.

When mature, the 2- to 2.5-inch 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. MRLS can cause late-term foal losses, early- and late-term fetal losses and weak foals. UK researchers conducted studies that revealed horses will inadvertently eat the caterpillars, and the caterpillar hairs embed into the lining of the horse’s alimentary tract. Once that protective barrier is breached, normal alimentary tract bacteria can 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 threat is greatest when the mature tent caterpillars leave trees and wander to find places to pupate and transform to the moth stage.

Eastern tent caterpillars are also a significant nuisance to people living near heavily infested trees. The caterpillars might wander hundreds of yards in search of protected sites to spin cocoons and pupate.

To get rid of active caterpillars, Townsend recommended 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. These types of insecticides are relatively nontoxic to humans. Spot treatments to the tents and the foliage around them can be applied according to label directions, which vary by product.

For more information about how to assess trees for egg masses, the UK Entomology publication “Checking Eastern Tent Caterpillar Egg Masses” is available at https://entomology.ca.uky.edu/ef449.

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