There are over 180,000 species of caterpillars in the world. One of them, the spongy moth, is in great abundance in Dutchess and Columbia counties this summer and has been wreaking havoc on local trees.
Until recently, the invasive species had been commonly known as gypsy moths. That was changed amid concerns the name denigrated ethnic Romani people. The current name, adapted from the French word for the moth, spongieuse, seems fitting. The spongy month first arrived in the United States from France in 1869.
Spongy moth caterpillars have voracious appetites, feeding on the leaves of a wide variety of trees including maple, apple, hickory, birch, pine, spruce, and their personal favorite, oak. Spongy moth infestations, which typically occur every 10-15 years, began their most recent cycle in New York state in 2020, reaching a peak in 2021. State conservationists believe the cycle is nearing an end, but for local residents watching the steady defoliation of their trees, spongy moths remain a crisis.
The spongy moth caterpillars begin eating their way through leaves from the moment they hatch in May. Male and female caterpillars both molt successive times, with males growing to 2 inches and females growing to 3. It’s estimated that a single caterpillar can eat up to 10 square feet’s worth of leaves over the brief course of its larval lifetime.
By June, the caterpillars begin to spin cocoons and enter a two-week pupation stage before transforming into moths and beginning the mating process. Spongy moths do not eat after emerging from their cocoons, and individual moths only live for a few days. Their focus is entirely upon reproduction. The females, which are unable to fly and simply look for an accessible place to cling to and display their white wings, attract males and lay a batch of eggs. A small egg mass that is an inch long might have 200 eggs and a large one of 3 inches long as many as 1,000. The sponginess of the egg mass comes from the hairs from the mother moth’s abdomen.
Maybe you’ve noticed a large number of small, brown-colored moths flying erratically. These are males following the pheromone scent trail of females whose eggs they are destined to fertilize.
The reproduction process is currently in full swing and will continue into August. After that, all of this year’s moth population will have died and all that remains are the egg masses that will hatch next spring.
Don’t despair if your yard has had tree damage. The damage done this year will, in most cases, be temporary. Trees are resilient. Some will begin sprouting new leaves this summer, helped along by the rain and sun. If the infestation recurs in three consecutive years, however, affected trees can be imperiled.
There are ways to help minimize the potential damage of next year’s spongy moth population. While male moths are difficult to catch and destroy, females are easy to spot and their egg masses can be removed and destroyed. Besides trees, egg masses are apt to be found on any hard, sheltered surfaces such lawn furniture and buildings.
The removal process is relatively simple and involves dispatching the female and carefully scraping off the egg mass and submerging it all in soapy water for at least two days. It is also possible to buy traps that disrupt the moths’ reproductive cycle altogether by using pheromones to lure male moths before they have a chance to mate. Ideally such traps should be hung in the spring, but remain effective as long as the moths are active, into the beginning of autumn.