What is the spongy moth, and what is it doing to our forests?

Spongy moth caterpillars have destroyed trees throughout the Tri-state region.
Peter Steiner
Spongy moth caterpillars have destroyed trees throughout the Tri-state region.
MILLBROOK — One of the major factors in the cycle of the spongy moth and their proliferation — or lack of proliferation — turns out to be acorns.
Spongy moths, formerly referred to as Gypsy moths for their itinerant ways, were the topic of a lecture Thursday, Jan. 11, by scientists Clive Jones, who has studied the spongy moth for 30 years, and Charles Canham, who has studied northeastern forests for 40 years. Both are emeritus scientists of Cary Institute of Ecosystems Studies, which hosted the lecture.
Spongy moths, natives of Europe and Asia, came to North America in 1868 or 1869, to Medford, Massachusetts. Amateur entomologist Etienne Trouvelot believed he could crossbreed them with silkworms in an attempt to “make a hardy silkworm.”
“He got some egg masses of the spongy moth and set them on the sill of his open window. When they blew into his garden, he could not find them,” said Jones.
By 1891, there was mass defoliation in the Medford area and spongy moths were found in a 200-square-mile area. From there, they began to spread throughout the U.S. and Canada.
Alone, the spongy moth travels by ballooning on silk threads; assisted, humans unwittingly transport eggs laid on cut logs or vehicles.
The life of the spongy moth could be said to begin in July and August, when the flightless female moths emit pheromones to tell males that they’re ready to mate.
They each lay a few hundred eggs, often at the bases of trees. If the moth population is high, they lay eggs anywhere, on garden furniture or on the bumper of a car.
Then, the following May, the eggs hatch. The larvae spend May and June ballooning to new locations on silken threads. They rest under trees during the day, then go up into the tree canopy at night to feed. They prefer oaks but also eat maple, beech, apple, hickory, willow and birch trees, among others.
When the population is very dense and the competition for food is fiercer, they may eat all day and night. Once a tree is defoliated, they’ll move to the next canopy.
In late June and July, the larvae pupate — a caterpillar-to-moth metamorphosis that lasts a couple of weeks — then they emerge and breed and the cycle begins again.
Jones explained that “outbreaks” — or high densities of spongy moths — “occur about every 10 years on average, but like any average, it does not mean there will be outbreaks like clockwork.”
There are two major causes of outbreaks, he continued. One is “high female fecundity,” for example: If one moth laid 500 eggs and 250 were female, 125 of those would live to maturity and lay eggs. So, in year two, there would be 125 females laying eggs, and the third year, over 15,000 would result.
The other cause of outbreaks is the collapse of the white-footed mouse population, he said. White-footed mice eat the pupae as a part of their omnivorous diet.
At this point, we reach the subject of acorns:
“The number of mice is determined by the number of acorns the previous fall,” Jones continued, saying that if there is a moderate to large acorn crop in the fall, more mice survive the winter and begin breeding earlier in the year, in late winter or early spring. When that happens, there is an extra generation of mice, meaning more mice to eat more moth pupae.
Studies at the Cary Institute concluded that “moderate to high mouse densities keep moth populations low,” while it was found “that when the mouse population declines, the spongy moth population increases.”
However, defoliation of oaks can cause the trees to produce fewer acorns, meaning less food for the mice, meaning fewer mice the following spring, meaning more moths, and so on, until the moth population collapses again.
There are three major causes of population collapse among the moths.
One is a fungus, Entomophaga maimaiga, which kills the moth at moderate and high densities. It likes cool, wet springs and is more abundant in those conditions.
The more common cause of collapse is Nuclear Polyhedrosis Virus (NPV): When the moths are at high density, they are more stressed by the struggle to find food. Their immunity drops, they are more likely to catch the virus, and many are killed.
The third cause of moth population collapse is lack of food: When they defoliate a large area of trees and run out of food too early, they can’t mature and proceed to egg laying.
Jones said that Cary Institute scientists predict an NPV collapse in 2024: “Whether or not there’ll be a lot or a little defoliation [this year] will really depend on how fast the virus moves through the population. If it moves slowly, there’ll be complete defoliation. If it goes through fast, there’ll be incomplete defoliation.”
Canham continued the lecture by saying, “Defoliation by caterpillars is rarely a direct and immediate cause of tree mortality.”
Canham explained that this is due to “carbohydrate economy”: “Basically, photosynthesis during the growing season produces the sugars needed to produce new tissues, and the energy those tissues need for their metabolism.
“But the even more important outcome of a good growing season is the profit leftover after meeting those immediate needs, and that profit is in the form of sugars and starches that act as reserves for use next year.”
Usually, unless the tree is weakened by other factors, it will draw on its reserves to get through this defoliation and produce more leaves that same year.
An exception that Canham has observed at Cary Institute is the understory hemlocks, which don’t make as many reserves and, after a couple years of defoliation in a row, may not recover. Needle trees, DEEP has noted, can be killed if they lose more than 50% of their foliate.
Canham said he worries more about the devastating effects of the emerald ash borer, longhorn beetle, spotted lantern fly and hemlock wooly adelgid than about the spongy moth.
He said if a tree is in crisis, a way to help it is to water it to “help replenish its reserves.”
For more information or to view the lecture video, go to www.caryinstitute.org/news-insights/lecture-video/...
AMENIA — The first day of school on Thursday, Sept. 4, at Webutuck Elementary School went smoothly, with teachers enthusiastically greeting the eager young students disembarking from buses. Excitement was measurable, with only a few tears from parents, but school began anyway.
Ready for her first day of school on Thursday, Sept. 4, at Webutuck Elementary School, Liliana Cawley, 7, would soon join her second grade class, but first she posed for a photo to mark the occasion.Photo by Leila Hawken
Millerton Police Chief Joseph Olenik shows off the new gear. Brand new police cruisers arrived last week.
MILLERTON — The Millerton Police Department has received two new patrol cars to replace vehicles destroyed in the February 2025 fire at the Village Water and Highway Department.
The new Ford Interceptors are custom-built for law enforcement. “They’re more rugged than a Ford Explorer,” said Millerton Police Chief Joseph Olenik, noting the all-wheel drive, heavy-duty suspension and larger tires and engine. “They call it the ‘Police Package.’”
Olenik worked with The Cruiser’s Division in Mamaroneck, New York, to design the vehicles.
“We really want to thank the Pine Plains Police Department for their tremendous support,” Olenik said. After the fire, “they were the first ones to come forward and offer help.”
The new police cruisers are outfitted with lights with automatically adjusting brightness to best perform in ambient conditions.Photo by Aly Morrissey
Since February, Millerton officers have been borrowing a patrol car from Pine Plains. With the new vehicles now in service, Olenik said he plans to thank Pine Plains officers by treating them to dinner at Four Brothers in Amenia and having their car detailed
The main entrance to Kent Hollow Mine at 341 South Amenia Road in Amenia.
AMENIA — Amenia residents and a Wassaic business have filed suit against the Town Board and Kent Hollow Inc., alleging a settlement between the town and the mine amounts to illegal contract zoning that allows the circumvention of environmental review.
Petitioners Laurence Levin, Theodore Schiffman and Clark Hill LLC filed the suit on Aug. 22. Town officials were served with documents for the case last week and took first steps in organizing a response to the suit at the Town Board meeting on Thursday, Sept. 4.
The lawsuit is the latest in a multi-year long legal battle surrounding the mine on South Amenia Road. After Kent Hollow Inc. — a subsidiary of Bethel, Connecticut, based homebuilder Steiner Inc. — applied for a state mining permit in 2017, the Amenia code enforcement officer issued the business a notice of violation.
At the time, Kent Hollow Inc. did not possess a special permit to conduct mining operations as required by Amenia zoning code, and the property did not reside in the Special Mining Overlay district established as part of rezoning efforts coinciding with the 2007 adoption of the town’s comprehensive plan.
Kent Hollow Inc. appealed the violation, claiming the use of the property as a mine predates amendments to town and state regulations. The Zoning Board of Appeals denied the appeal citing insufficient evidence in 2019. That spurred Kent Hollow to file two lawsuits — one in the New York State Supreme Court and a federal civil rights lawsuit — challenging the town’s order.
In July 2025, those lawsuits were brought to a close when the Town Board voted at a special meeting to accept a settlement agreement allowing Kent Hollow to continue mining operations under limited hours and quantities.
The most recent suit alleges the 2025 settlement amounts to contract zoning that allows Kent Hollow Inc. to skirt environmental review and the scrutiny of the permitting and rezoning process. Court documents allege Kent Hollow did not adequately prove a continuous, legal nonconforming use.
Supporting the argument, petitioners have submitted the court documents and decision from the 2019 New York Supreme Court case against the town Zoning Board of Appeals, and the documents from the preceding ZBA appeals process including receipts and tax returns from Kent Hollow Inc. purporting to establish the nonconforming use.
Kent Hollow Inc. formed as a subsidiary of housing developer Steiner Inc. and purchased the property in 1971, according to state and county real estate records.
Millerton News reporting from 1971 Amenia planning board meetings detail Kent Hollow’s pursuit of a four-section, 40-unit apartment complex on the property.
The News reported Kent Hollow was granted tentative approval on July 6, 1971, to build eight units on the site with the expectation that more would be built later.
The additional units never came to fruition and Kent Hollow apparently abandoned the housing project, opting to use the property as a gravel mine.
Attorneys for the Town of Amenia or Kent Hollow Inc. have not filed responses to the lawsuit as of press time.
AMENIA — While the courage and perseverance of Revolutionary era patriots is well understood and celebrated, the stories of the fate of British loyalists in New York are not as clear.
Seen as the initial event in observance of the 250th anniversary of the American Revolution, the Amenia Historical Society will present a talk titled, “The Plight of a Loyalist in Revolutionary New York,” examining the journal of Cadwallader Colden, Jr., spanning the period of 1777-1779. The speaker will be noted author, genealogist and historian Jay Campbell.
The talk is scheduled for Saturday, Sept. 27, at 2 p.m. at the Smithfield Presbyterian Church in Amenia. The handicapped-accessible church is located at 656 Smithfield Valley Road. Refreshments will be served.
Colden was the son of a New York Lieutenant Governor. He was a surveyor, farmer and mercantilist, serving as a judge in Ulster County. His fortunes changed dramatically with the dawn of the Revolutionary War when he remained loyal to the British Crown. His arrest came in 1776, just before the start of his journal.
Campbell is a historian specializing in Hudson Valley history, and the regional stories of Revolutionary era families.