Very soon, we will start to see little green caterpillars hatch from eggs lain in the bark around the base of trees make their way up into the canopy, where they will chow down on buds and leaves. Once eating their fill, they spin a string of silk and drift onto their next victim. They will migrate from tree to tree and may also drop into nearby shrubs. A tree can be almost stripped clean, or may just have a few holes in the leaves. It all depends on how heavily infested an area is – and that can vary greatly even within one neighborhood.
What goes in must come out, which means that while these greedy green critters are munching away on your prized maple trees, they are pooping little black granules all over your yard. Once feeding season is over in mid-June, caterpillars head underground until November, when the moths hatch and we will see them fluttering around our lights again.
While their feeding period is only about 6 weeks long, Winter Moth caterpillars can strip a tree of its foliage, leaving it weak and susceptible to other diseases, as well as reducing its overall growth rate. After a few years of attack, it can kill a tree.
So what can be done?
Entomologists and Forest Managers are finding some success in controlling Winter Moths by releasing a parasitic fly, called Cyzenis albicans, which also originates from Europe. The fly lays its eggs on foliage that the Winter Moth caterpillars eat. The eggs hatch inside the caterpillar and develop into a larval fly. When the caterpillars return to the ground, they soon die, and a new parasitic fly will emerge in the Spring. Think Alien for bugs, and Sigourney Weaver is an entomologist. UMass Amherst has been working on controlling Winter Moth at several sites in Massachusetts, Maine, and Rhode Island over the past few years, and seeing marked reduction in Winter Moth populations year over year.
Read more about this project here
In your own yard, enlisting the help of a Certified Arborist may be your best bet. There are some treatments available, but timing of applications is specific. If your trees are particularly stressed after Winter Moth feeding, additional watering will help support new growth.