The spongy moth (Lymantria dispar), formerly known as gypsy moth, has been a problem species in the United States since they were introduced in 1869. An amateur entomologist from France named Léopold Trouvelot introduced spongy moths in Massachusetts from its native range of Europe and Asia, in hopes of introducing a disease resistant silk producing caterpillar. This idea did not pan out, and resulted in caterpillars escaping from their enclosure in Trouvelot’s backyard, creating the spongy moth problem we have today. Since their introduction in 1869, spongy moths have resulted in the defoliation of millions of acres of trees throughout the United States. These moths have spread from Massachusetts to most of the northeastern United States including all neighboring states to Indiana.
Caterpillars of the spongy moth can be characterized by being dark gray/black in color, are hairy as young larvae, and have gray bristlelike hairs and red and blue dots along the length of their body as they mature. The moths are characterized by the males being light brown and dark bands along the wing and females being larger in size than males and white in color.
The spongy moth is an invasive species that will defoliate a tree, resulting in the tree becoming more vulnerable to disease and additional pests. This defoliation is pictured below featured on one of our Paper Birch trees (Betula papyrifera) in the Birch Grove of the Event Garden.
This invasive species has over 150 primary hosts but can feed on more than 300 species of trees and shrubs. Female moths lay egg masses from June to July and the eggs hatch in April and May (these egg masses are pictured below on a Willow (Salix sp.)).
Young larvae chew small holes into leaves of the host plant, while larger older larvae can consume entire leaves, resulting in rapid defoliation of trees. If the spongy moth larvae life cycle continues in an area, repeated defoliation can result in death of a tree. The spongy moth has favored host trees including oaks, alder and apple trees and less favored hosts including hickory, maple and cherry. At Wellfield Botanic Gardens, we have found egg masses on oaks, hickories, cherries, birch and willow. We have even found eggs on trash cans, decorative pots and on buildings! Through our observations, it seems they tend to lay eggs on objects close to a primary host species, as the trash cans, buildings, and less favored trees were within close proximity to oaks.
In order to prevent spongy moths from hatching, eggs should be gently scraped off and crushed. Simply scraping them onto the ground (without crushing them) can result in them still surviving into the next year. Egg masses can contain more than 600 eggs, so destroying any you see can help reduce the population of the spongy moth for next year! Spraying the egg masses with horticulture oil labeled for use on spongy moths can also be used as well as applying pesticides. At Wellfield Botanic Gardens, we are limited in the practices we can use due to being on a well field, but this past year, we crushed as many of the egg masses that we could to try and limit the number of spongy moths this season. There are plenty of different practices that can be applied so it all comes down to what you feel comfortable doing. We can try our best to reduce populations in our area to ensure the lives of not only the trees themselves but also all organisms that call the trees their home. So, watch out for caterpillars in your area (and the egg masses that are soon to come in June and July) and work towards eradicating this invasive species.
Ariana Guerrero
Horticulturist
