For a second summer in a row, it appears that the pesky Spongy Moth (formerly “Gypsy Moth”) will have an impact on the region’s forests.
Spongy moths, Lymantria dispar, were first introduced to the U.S. from Eurasia in 1869, with the intention of using the species for silk production. The species failed to produce silk and without a natural predator in the U.S., the insect spread through the Northeast and into the Mid-Atlantic and Midwest.
In their caterpillar phase, spongy moths prefer to eat the foliage of oak species. In years of high spongy moth populations, they will also feed on the foliage of other deciduous trees and even evergreen needles. Otherwise healthy deciduous trees can survive 2-3 years of defoliation. These trees will usually lose their leaves to caterpillars in the spring, and re-leaf during summertime. Conifers that lose only some needles can typically survive as well; unfortunately, conifers that lose all their needles due to spongy moths will likely die.
If trees look dead and bare, the expert recommendation is to wait a year and see if the tree regains health and regrows, as long as the tree is not in a position that would cause property damage or injury.
Generally, spongy moth populations rise and fall in 15 year cycles. The “outbreaks” of spongy moths typically last two years before the numbers begin to drop again. Spongy moth populations are controlled by a bacterium found naturally in the soil, Bacillus thuringiensis, also called Btk, which can be purchased as a foliar spray for population control. There is also a virus that kills spongy moth caterpillars.
The species was recently renamed to better reflect the moth’s sponge-like egg masses in which the insect will spend most of its’ life, and to move away from the former name which derived from an outdated, ethnic slur.
Female spongy moth and an egg mass.
Spongy moth caterpillar.