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Gypsy moth caterpillars ‘get active’ again on Long Island, experts say

Gypsy moth caterpillars munch up breakfast, lunch and

Gypsy moth caterpillars munch up breakfast, lunch and supper on Saturday, June 4, 2016, in Heckscher State Park in East Islip. Photo Credit: James Carbone

Last year’s infestation by tree-leaf-gobbling gypsy moth caterpillars was described in July by an entomologist as “the largest I recall since 1988.”

This year’s crop, the progeny of last’s, could well amount to more of the same.

Dan Gilrein, entomologist with Cornell Cooperative Extension of Suffolk County, said he’s gotten reports of noticeable infestation, with “very apparent defoliation” in areas around Connetquot and Heckscher state parks in Islip town.

Already Evan Dackow, certified arborist, has been out on calls, Friday morning visiting a commercial property in Smithtown where “the ground was covered with cut leaves,” dropped from munching caterpillars on tree branches above.

“They’re starting to get active — they’re making a showing again,” said Dackow, co-owner of Jolly Green Tree & Shrub Care in Farmingdale, who’s also heard from customers in Patchogue and Bay Shore.

Last year’s bumper crop followed an especially dry spring, with May breaking the record for lack of rain. That created favorable conditions for eggs, laid the previous year, to develop and for caterpillars to flourish.

Ordinarily, sufficient precipitation has led to the growth and spread of a natural gypsy moth-killing fungus, which Gilrein wrote in a blog post last August, “has done a good job of regulating its population since 1988.”

Fast forward to this year, which saw a metrological spring — March, April, May — registering a 3.84 inch precipitation deficit. According to the U.S. Drought Monitor, Long Island is in its “abnormally dry” and least intense category.

That would be good news if you were among the many eggs that hatched around April — with close to a two inch rain deficit — and are now hungry, bristly caterpillars, well-over-an-inch long and dotted with blue and red spots.

With a dearth of biological control, last year’s insects “bred like crazy,” with their eggs hatching into this year’s dry conditions, said Dackow. Infestation he saw last year “was horrible,” especially in areas around Northport, Smithtown, Bay Shore, Patchogue and the Hamptons. He’s expecting heavy infestation again this year.

Based on last year’s presence, “a moderate to heavy infestation” is anticipated this year, according to experts from the state Department of Environmental Conservation. They say, too, that the gypsy moth should not be confused with the native tent caterpillar, abundant this year and especially partial to black cherry trees.

The good news is that gypsy moths at this stage are susceptible to organic and conventional pesticide spraying, Dackow said.

On Long Island, spraying should be done from late April through early June, perhaps a week or two later on the Twin Forks, according to Suffolk’s Cornell Extension website.

The impact of an infestation can be startling, with damaged, leafless trees looking more like those of January than of July.

A heavily infested tree can be “a little creepy looking,” Dackow said, as the caterpillar-covered trunk can appear to be moving slightly back and forth.

Trees can survive a hit, experts say, because they’re programmed to grow a second leaf covering. But that uses up much of the trees’ backup nutrients, leaving them especially susceptible to other stressors. Among those could be “other defoliators,” such as the orange-striped oak-worm or fall webworm that arrive later in the summer, Gilrein said.

Not native to the United States, the moths were introduced in 1869 with hopes of their breeding with silkworms and an eye to establishing a silk industry, according to the DEC’s website.


  • Eggs, laid in July or August, hatch the following spring
  • That’s right around when buds on oak trees start opening.
  • Other dining fare can include maple, apple, aspen, willow, birch, mountain ash, pine and spruce trees.
  • Caterpillars grow to about 2 1/4 inches
  • Around June and early July, they become pupa, then adults
  • Males fly around, females don’t
  • After mating and just before dying, females in July and August lay a mass of from 100 to 600 eggs.

Sources: NYS DEC, Cornell Cooperative Extension of Suffolk County

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