Spongy Moth (Lymantria dispar, formerly gypsy moth)
What is a Spongy Moth?
Formerly known as “Gypsy Moth,” Lymantria dispar is found most often in its caterpillar stage, where it is a voracious eater of many different tree species’ leaves. Its preferred host is oak trees but it can also commonly be found on Colorado Blue Spruce, Basswood, and Apple trees. The caterpillars are most active during dawn and dusk but will remain feeding continuously until they pupate. After pupation, the adults do not feed any longer and exist solely to mate and lay eggs.
How did They Get to America?
No, Spongy Moths are not native to Michigan. The spongy moth originally hails from Eurasia and was introduced to North America in the 1860s. Etienne L. Trouvelot, a French entomologist in Medford, MA, accidentally released spongy moths while experimenting with various species for silk production. Since then, the moth has become a significant pest in North America, causing extensive damage to various tree species. Early control efforts, including widespread pesticide use, were largely ineffective. Eventually, the introduction of the maimaiga fungus provided a more successful biological control method. Despite this, periodic outbreaks still occur, stressing trees and leading to secondary pest issues.
Spongy Moth Predators
Several native birds feed on Spongy Moth caterpillars, and some rodents prey on the larvae and pupae. However, this predation is not sufficient to control outbreaks during large infestations.
Currently, there is a fungus present in Michigan soils that helps control caterpillar populations, called Entomophaga maimaima. Infection from this fungal disease causes caterpillars to seek high places, where they then burst with spores and spread them to other Spongy Moth caterpillars. This treatment is highly effective when environmental conditions are right: cold and wet springs. The fungus relies on moisture to spread.
Weather is such an important factor. Dry springs are bad for fungal growth, so contribute to rising Spongy Moth populations. Warm and wet summers are ideal for insect growth and can cause moth populations to outgrow the pace of fungal infection. Climate change makes regular weather patterns even more unpredictable.
Many areas of Michigan are experiencing 3 years or more of Spongy Moth outbreaks which may be causing considerable damage to trees in these areas.
How to Get Rid of Spongy Moth Caterpillars
When will It End?
Their Life Cycle
The nastier effects of the moth’s presence will stop. The Spongy Moth has a defined life cycle consisting of several stages. It begins with the egg stage, where each mass contains approximately 600 eggs. These eggs hatch into larvae that feed continuously and cause severe to complete defoliation of trees.
While it may seem like an eternity during the feeding, thankfully, the caterpillars are a short-lived portion of the moth’s life cycle. The caterpillar stage only lasts 7 to 8 weeks.
Following this, the larvae enter the pupal stage for 1 to 2 weeks in June or July, undergoing metamorphosis. After pupating, the adult moths do not feed. Adult males emerge solely for mating. After mating, each flightless female moth can lay between 600 and 1000 eggs in a single egg mass. These are placed in dark and protected areas, such as the underside of branches, the crooks of trees, awnings, and gutters.
Destroying any egg sacs you can see will help reduce the viable population for the following year.
