The spongy moth, Lymantria dispar dispar, is an invasive insect known for its defoliating activity. This species, originally from Europe, was accidentally introduced to North America in 1869. The insect’s common name was officially changed to spongy moth in 2022. The diet of spongy moth caterpillars consists almost entirely of tree leaves, making them a significant concern for forest health.
Preferred Tree Species
Spongy moth caterpillars exhibit a strong preference for certain tree species, on which they thrive and cause the most significant damage. Oaks, including various species, are consistently listed as highly favored hosts. The abundance of oak in many North American forests contributes to the impact of spongy moth outbreaks. Beyond oaks, other preferred deciduous trees include apple, sweetgum, speckled alder, basswood, gray and white birch, poplar, willow, hawthorn, and linden. These trees provide an optimal food source for the caterpillars, allowing for their rapid development and population growth.
Other Consumed Plants
While certain trees are preferred, spongy moth caterpillars can feed on a wide variety of plant species, especially when their favorite hosts are scarce or during large outbreaks. Over 500 species of trees and plants can serve as food sources for these caterpillars. This broader diet includes other deciduous trees like maple, cherry, elm, beech, and hickory.
Conifers such as pine, spruce, and hemlock are also consumed, particularly by older caterpillars. Some shrubs and garden plants can also be defoliated during periods of high caterpillar density. However, some species, including ash, black locust, fir, holly, juniper, redbud, sycamore, and tulip tree, are generally avoided, with caterpillars rarely feeding on them.
How Spongy Moths Feed and Their Impact
The damage caused by spongy moths is exclusively from their larval, or caterpillar, stage. Adult moths do not consume foliage; their primary role is reproduction. Newly hatched caterpillars are small and black, chewing minor holes in tender new leaves. As they mature, caterpillars grow significantly and can consume entire leaves, often leaving only the tough midribs.
This extensive feeding leads to defoliation, which can weaken trees, reduce their growth, and make them more vulnerable to other pests and diseases. Deciduous trees, which shed their leaves annually, can often regrow a new set of leaves after defoliation, particularly if it occurs early in the season. However, repeated heavy defoliation over two to three consecutive years can lead to tree mortality. Conifers, which retain their needles year-round, are more susceptible to death from a single severe defoliation event because they do not easily regrow their foliage within the same season.