You are facing a tall Red Oak, an impressive tree, but also a favorite food source for the caterpillars of an invasive moth. The Spongy Moth (previously called Gypsy Moth) was introduced from Europe to Massachusetts in 1869 when it escaped the lab of an amateur entomologist. In New Hampshire, outbreaks of this species have occurred every 7 to 10 years since 1924. 

Spongy Moth caterpillars can feed on oak trees in huge numbers, defoliating them in a matter of just a few weeks. If the trees are strong and defoliation happens early enough in the season, they will re-grow leaves by the fall. But resprouting uses much of the energy that these trees might need for the following year. Some oak trees can be killed by repeated years of complete defoliation.

Spongy Moth caterpillars are easily recognized, especially as they get larger. They have five pairs of dark blue dots and six pairs of bright red dots running along their hairy backs. In mid to late July, you will begin to see the tan adult moths flying, but these are only the males. Female moths are a lighter-color, almost white. But the females rarely fly. Instead, they wait, usually on a tree trunk where the males find them, and then they mate. Adult moths only live about two weeks.

While this invasive moth can cause a lot of damage, there is hope for limiting its impact on our forests. Spongy Moth predators include rodents, birds, parasitic wasps, and spiders. Early in the 20th century, a non-native fungus was imported from Japan to try to kill the moth, at the time without known success. But more recently, in 1989 in New Hampshire, Vermont, and Connecticut, scientists found that this fungus, Entomophaga maimaiga, had successfully killed some moth larvae, and so it remains an important potential tool against Spongy Moth outbreaks.

Reader: Chris Martin