The moths have cometh (and what you may be able to do about it)

Tips on dealing with Spongy Moths this summer

story and photos by niki@hvny.info
originally published July 10, 2023; updated May 2, 2024

Spongy moths – formerly known as gypsy moths, an invasive species from Europe that escaped a backyard in Massachusetts around 1868 – have now hatched in full force here the Hudson Valley, and they may hang around into August.

In the summer of 2023, the valley’s picturesque vistas showed visible signs of their wear: trees on parts of the Taconic in northern Dutchess and Columbia are bare – not from drought, but from defoliation: the incessant munching by those hungry, hungry caterpillars. They have now emerged as moths. The males are the ones fluttering about the base of oak trees, apple trees and other hardwood species (more on that below), while the female moths don’t fly, but are laying masses of eggs in between the groves of the bark on these trees, ensuring their invasive legacies.

The City of Hudson even sent out a “Moth Advisory” to residents, though noting “that recommendations included in this advisory may protect individual or small areas, but they will not erase a local spongy moth population now or in future years.”

But there’s good news on the horizon, especially with all this rain: Some trees may re-foliage by mid-summer “even after experiencing more than 50 percent defoliation,” according to the USDA. And weather, white-footed mice, as well as fungal and viral disease can also help combat the spongy moth population for future summers to come.

What to look for:

Adult female spongy moths are white with brown markings, they do not fly and are usually on a tree, on the ground or at the base
Adult male spongy moths are brown with black markings
Spongy moth egg masses are brown clumps
The caterpillars have two rows of colored spots: five pairs of blue and six pairs of red

How to (try to) get rid of them:

NOTE: Spongy moth caterpillars, moths and their egg masses carry histamines that can irritate the skin, causing an itchy rash in some individuals.

For manual removal, wear gloves and knock the caterpillars or moths into a bucket of soapy water (or squish ‘em). This is method, though, is impractical for large, infected areas and can be reserved for protecting key trees in your yard.

Wrapping a 12-inch burlap strip around your tree with a string can also trap caterpillars traveling up the tree. After they get stuck in the burlap, they can then be knocked into a bucket of soapy water. Sticky traps and pheromone trapping are also available. (The DEC does not typically manage spongy moths, with treatments reserved to ecologically or culturally significant forests.)

Spongy moth larvae are affected by a viral disease and fungal infections. If you find diseased larvae – larvae killed by viruses look like V's, larvae killed by fungi hang head down – leave them be so that other larvae will also be infected.

White-footed mice and other small animals feed on both the larvae and pupae, and are typically “the most important cause of spongy moth mortality in low-density spongy moth populations.”

Clean your shoes and tools afterwards to help prevent the spread of their eggs. Check your clothes if you hang them to dry outside, and turn off outdoor lights near doors so you don’t attract male moths into the house.

Will your tree(s) survive?

If your tree is healthy, it can withstand defoliation for 1-2 years. Some trees may even re-foliage by mid-summer after 50-percent defoliation. A single defoliation can kill some evergreens, but usually two or more defoliations are needed to kill hardwood trees. Defoliation will weaken trees, leaving them more susceptible to other disease and damage.

What tree species do spongy moths like/dislike:

Spongy moths like: Oaks, willow, apple, crabapple, white birch, witch hazel, mountain ash, basswood, linden, pine, Douglas fir and spruce.

Spongy moths (generally) avoid: Ash, balsam fir, locust, Scotch pine, red cedar, tulip poplar, catalpa, sycamore and dogwoods.

Will/when will they be back?

“Spongy moth populations rise and fall in cycles,” says Joyce Tomaselli, Cornell Cooperative Extension of Dutchess County Community Horticulture Resource Education, “specifically caused by the interactions between spongy moth, small mammals and acorn production. Natural causes such as fungal and viral diseases usually knock down populations in a few years. Weather is also a factor.”

And as of May 1, 2024 – tiny spongy moth caterpillars hatched, and are back with a vengeance. But unfortunately, there’s nothing we can really do about it. (Though Dawn dish soap in a spray bottle with warm water seems to do the trick for small populations on our outdoor furniture.)

“Because the infestation is so large and the caterpillars drift through the air on web-like silky strings, the treatments that typically come to mind are not effective. Scraping the egg sacks off your trees, using sticky tape or burlap bands around the tree, and spraying trees with pesticides will not help in most situations.

A naturally occurring virus and fungus will likely kill the caterpillars and should bring the population back into balance either this year or next at the latest.”