March 20, 2002 | By: Haven Miller

Eastern tent caterpillar egg hatch has started in Kentucky. Although it is two weeks earlier than last year, its timing is right on the historical average which usually corresponds to 50 percent Forsythia bloom.

Questions about how soon egg hatch will be completed and when tent caterpillars will begin to feed will soon be answered by Kentucky's spring weather.

"When temperatures are in the upper 70s most of the eggs hatch in eight to ten days, however, highs in the 50s can spread hatch out over a month," said Lee Townsend, Extension entomologist in the University of Kentucky College of Agriculture. "These caterpillars are basically inactive below 50 degrees so it's easy to see how great an effect temperature has on them."

The tent caterpillar, which gets its name from the silken tent it constructs in tree branches, prefers wild cherry but also feeds on peach, apple, crabapple and other trees.

"Moths, the adult stage, laid lots of eggs on twigs of those trees last summer, and this points to many tent caterpillars again this year which will be the third consecutive year of large populations," said Townsend. "This insect, which is common throughout the eastern United States, is a nuisance but poses no health threat to humans."

Because the eastern tent caterpillar has been identified as one of the risk factors associated with Mare Reproductive Loss Syndrome, UK scientists are intensely monitoring its activity. As part of a comprehensive UK program this spring scientists also are watching other factors, including pasture conditions and weather patterns.

"Naturally, research on the eastern tent caterpillar is continuing," said Townsend.

Townsend said farm owners and homeowners who intend to manage this insect should not treat at this time. It is important to wait for most eggs to hatch before starting a control program. The caterpillars need to be out and feeding for control to be effective. In some cases simple mechanical removal and destruction of nests may be sufficient.

"A patient approach will allow any early natural control, such as heavy rains or freezes, to have an effect, and we need to keep in mind that treating too early can mean that additional applications may be needed," Townsend said. "Spraying will be most effective when the nests are established and the caterpillars are actively feeding. Waiting until the nests are about the size of a baseball or softball should be about ideal."

Townsend said more detailed control recommendations will be forthcoming from the UK College of Agriculture as the time for treatment approaches. He also said county offices of UK's Cooperative Extension Service are an excellent source of information on insect pest management, as well as the UK entomology department's web site at


Lee Townsend, 859-257-7455