Eastern Tent Caterpillar Eggs Could Hatch Early in Kentucky

An Easter tent caterpillar egg mass.

Photo: University of Kentucky's College of Agriculture, Food, and Environment

Eastern tent caterpillars will likely begin to hatch soon, said Lee Townsend, PhD, University of Kentucky (UK) College of Agriculture, Food and Environment extension entomologist.

“Eastern tent caterpillars are among the first insects to appear in the spring,” he said. “Consequently, they can cope with the erratic temperature swings that are common in Kentucky. This year’s unseasonable warmth points to abnormally early activity.”

Eggs from a mass Townsend collected on Feb. 17 hatched after a weekend indoors.

“Although the temperature was artificially high (in the lab), clearly (outside) conditions are close to prompting eastern tent caterpillar hatch,” he said. “In addition, black cherry leaf buds are starting to open. High and low temperatures from Feb. 17-24 are about 20 degrees above seasonal normal. Egg hatch this year may beat the previous record soundly.”

That record, Townsend said, was March 14, 2012. The latest observed hatch since 2011 was April 4, 2013.

Arborist Larry Hanks has provided first observed egg hatch in Scott County since 2011.

“It is important for horse farm managers to keep these hairy caterpillars in mind and, barring a significant weather change, to begin watching early for developing tents,” Hanks said. “If the warm weather continues, they may become visible in black cherry trees in pasture and paddock tree lines in seven to 10 days.”

When mature, the 2- to 2 ½-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 1999-2001 outbreak of mare reproductive loss syndrome, which can cause late-term foal losses, early- and late-term fetal losses, and weak foals. Researchers from UK 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 black 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 can wander hundreds of yards in search of protected sites to spin cocoons and pupate.

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. 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.

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

Holly Wiemers, MA, APR, is communications and managing director for UK Ag Equine Programs.

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