LEXINGTON, Ky. — Horse owners have come to realize the dangers Eastern tent caterpillars pose to their animals; they just didn’t expect to see them so early this year.

The unusually warm winter has caused an early arrival for this insect that is most recognized by its silken-like tents, found in host trees such as apple and wild or ornamental cherry, and occasionally on pecan, hawthorne, beech and willow, according to information from the USDA.

While the caterpillars, which show up each spring, rarely cause those trees to die, they are capable of wreaking havoc on the horse industry. Mare Reproductive Loss Syndrome (MRLS) cost the equine industry an estimated $336 million. This affected all breeds and approximately 30 percent of the 2001-02 Thoroughbred foal crop when the insect was first discovered – all thought to be caused by accidental ingestion of Eastern tent caterpillars by pregnant mares.

It is the hair on the caterpillars that becomes embedded into the lining of the horse’s alimentary tract, creating the possibility of fetal death. Lee Townsend, University of Kentucky (UK) College of Agriculture entomologist, thinks the first insect tents should show up by the end of the week.

“We’re probably at least two to three weeks early in terms of when the tents show up, but it all depends on our spring weather and of course, tree and plant development that is moved along, as well,” he said. “The insects pretty well stay synchronized to what is going on with the plant they’re feeding on.”

Townsend added the caterpillars grow and develop as long as the temperature is above 37 degrees; the warmer it is, the faster they will grow. While cold temperatures will slow them down, their tent and the general hardiness of the species will keep them from being affected drastically, even if temperatures drop below freezing at night.

This year’s winter season has been anything but winter, with warmer than normal temperatures and little snowfall except for higher elevations in eastern Kentucky. The warmer conditions have caused spring flowers to pop up early and trees to bud. But it doesn’t mean there will be more caterpillars than usual.

Townsend said the populations seem to go in cycles, with the heaviest infestations coming in approximately 20-year intervals. In between those big peaks, however, are gradual buildups in locations where natural enemies aren’t as prevalent or where there are more cherry trees.

“What we have seen are locally heavy populations, not with particular patterns,” he said. “Some parts of counties you see quite a bit of Eastern tent caterpillar activity, others it’s quite rare.”

Starting in 1999 through about 2001, Townsend said the caterpillar populations were at a peak, which coincided with major losses of foals. In early research, a variety of causes were examined but once the focus turned to the caterpillar and the cause was determined, horse farm owners became vigilant in checking for the insects, in many cases removing host trees.

“The main thing is to have horse owners, particularly with pregnant mares, just keep an eye on their situation and work to keep exposure of pregnant mares to a minimum,” Townsend said.

“I think the main thing, if you assess and do find that your populations are high and mares need to be kept pastured where tents are active, the thing to do is use the biology of the insect against it.”

He suggested to take any control measures while caterpillars are still on the trees since once they leave, it’s almost impossible to stop them. “While they are on the trees you can do anything from physical removal to direct treatment with insecticides,” Townsend explained.

If there is a bright side, it could be that cold weather is still a real possibility, which could harm the caterpillars. Townsend said the foliage on wild cherry trees is the primary diet of young caterpillars and in the event a cold spell kills that foliage, it would deprive the insects.

“Those caterpillars that are out are going to be small and there’s a good possibility that a pretty good number of those are going to die without the right kind of food,” he said. “When the caterpillars are bigger, they can feed on a number of different kinds of tree leaves, but when they’re small they’re pretty well locked in to wild cherry. If you’ve got most of the foliage burned, it could work to our advantage to provide some control.”