Gypsy moth caterpillars -- bristly, dotted with blue and red spots and known for denuding trees of their leaves -- have been present en masse this spring and early summer on Long Island, experts say.

While there have been previous, more localized outbreaks, this year's gypsy moth presence "has been the largest I recall since 1988," said Dan Gilrein, an entomologist with Cornell Cooperative Extension of Suffolk County.

One factor contributing to this year's outbreak was May's record-breaking lack of rain.

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"The dry month of May created perfect weather for insect development," said Daniel Kepich of the U.S. Department of Agriculture's Animal and Plant Health Inspection Service in New York.

Naturally occurring fungus and disease that ordinarily control the gypsy moth "grow and spread in wet environments," a USDA spokeswoman said. June's near-normal rainfall "was too late for natural controls to keep the gypsy moth population down."

Gypsy moths usually are an "insignificant" problem on Long Island, other than in very localized spots, said Evan Dackow, a certified arborist and co-owner of Jolly Green Landscaping in Farmingdale.

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But around mid-June he started getting calls from people in Suffolk as the caterpillars were reaching 2 inches in length and partially eaten leaves were piling up on lawns. After that, he said, his firm started spraying at around 40 to 50 locations, more than doubling his regular clientele for gypsy moth treatment.

At least 100 acres in the area of Heckscher State Park and Connetquot River State Park Preserve appeared to be affected, Dackow said.

Among the locations Gilrein cites with visible defoliation are Heckscher State Park, spots off the Southern State Parkway at Robert Moses Causeway and the Northport/Smithtown area.

"I do think this is a peak year," said Vincent Drzewucki of Cornell's Nassau County extension. He said he's recently seen caterpillar presence, but not defoliated trees, in areas north of Jericho Turnpike.

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

The trees can survive, 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.

"There will be a bigger problem if we see late-summer pests, such as orangestriped oak worm, arrive to cause a second wave of defoliation," Gilrein said.

Gypsy moth eggs, which are laid in the summer, hatch the following spring about the time oak tree buds start to open, providing "tender new leaves" for young caterpillars to eat, according to the state Department of Environmental Conservation website. Other trees that can be affected include maple, apple, aspen, willow, birch, mountain ash, pine and spruce, the DEC says.

At this point, with most of the damage already done and caterpillars on the cusp of the pupating stage, spraying would not be effective, said Drzewucki, who points also to the cyclical nature of gypsy moth outbreaks.

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Spraying should be considered for next year, though, he said, from late April to early June.

That, and spotting and scraping off sacs of eggs -- described by the DEC as "buff-colored, fuzzy patches" -- that could be attached to tree trunks, branches and even lawn furniture.