The Return of the Gypsy Moth Caterpillar

School’s out. It’s vacation time — time for summer camp, the great outdoors, hiking in the woods, and so on.

One thing we might notice during our time in the great outdoors is that for Hashem’s creatures, there is no such thing as vacation. They are constantly busy.

In New England this time of year, the gypsy moth caterpillar is especially hard at work, growing from a hairy little creeper to mature moth-hood. To fuel that growth it eats leaves. Due to recent dry weather, the natural enemies of the gypsy moth caterpillar (like Entomophaga maimaiga, a Japanese soil fungus that thrives on moisture) have gone into decline. As a result, their natural prey, the gypsy moth caterpillar, has been proliferating – and that’s bad news for the trees.

At this very moment, the gypsy moth caterpillar is busily at work destroying the leaves of trees. The critter isn’t fussy about its food, either, so a wide variety of species are at risk, including oaks, aspen, apple, sweetgum, speckled alder, basswood, gray, paper birch, poplar, willow, and hawthorn. Entomologists say the furry creature can feed on any of 300 different species of trees.

In large swathes of Massachusetts, Connecticut and Rhode Island, you can actually hear them chewing up the foliage at night.

In 2015, the caterpillar reportedly devoured more than 175,000 acres in Connecticut alone, in the worst outbreak since 1981, according to Joseph Elkinton, an entomologist at the University of Massachusetts/Amherst. In that year it defoliated more than 200,000 acres of Massachusetts hardwood, and millions more nationwide.

The state sprayed pesticides to control them until 1989, when a fungal pathogen brought the gypsy moth caterpillar population back down to reasonable proportions.

Now dry-to-drought conditions have again caused a population imbalance, and with the same devastating effects.

“It’s everywhere,” Elkinton said. “You can hear the frass falling,” he added, using the scientific term for caterpillar droppings. “And you can hear the chewing; it’s quite a dramatic phenomenon.”

That’s an indication of the scale involved. In the larva (caterpillar) stage, they are a miniscule 0.11811 inches in length when hatched, and will only reach 1.97 to 3.54 inches at most. The sound of these tiny guys chewing on leaf hairs and leaf epidermis is not like a human crunching through a bag of popcorn.

You wouldn’t hear a single gypsy moth caterpillar chewing a leaf, even the loudest among them. You need millions and millions of them masticating together to produce an audible sound.

They are so small and light that when the time is right, the larvae, hanging on the undersides of leaves from silken threads, are carried by the wind. Long hairs designed to increase their surface area help keep them aloft.

Their metamorphosis from caterpillar to moth, in the famous silky cocoon, is an amazing event, which most of us have probably never seen in real life. That’s because it’s a relatively hidden miracle, taking place under flaps of bark, in crevices, under branches, and on the ground. Sometimes, though, in times of population surge, it can happen in the open, on the trunks of trees.

The consequences of overpopulation of the gypsy moth caterpillar are not just aesthetic, even if the huge bare patches left by them would be reason enough for concern; the denuded trees also become vulnerable to various pests and disease, as well as forest fires. In Rhode Island, the state’s Department of Environmental Management recently warned the public to take extra care not to spark fires while cooking outside or using fireworks.

The caterpillars have been so numerous as to cause consternation. An allergist in Rhode Island said the little hairs on their bodies can attach to human skin and cause a “histamine-type reaction” that could last for days or weeks.

A distraught teacher in southeastern Massachusetts called the forest health program at the state Department of Conservation and Recreation to complain that several of her pupils got rashes from touching the spiny hairs of the caterpillars, which had fallen from trees into the playground. The teacher wanted to know why the state hadn’t taken care of this public health hazard.

Officialdom had no answer. As Elkinton said, “There is really not much that can be done, not now. We don’t have any magic bullets.”

Aerial spraying is expensive and ecologically a problem because it can kill innocent species of moths and butterflies, along with the notorious gypsy caterpillar.

This season of the gypsy moth caterpillar is coming to end, though. And with sufficient rain, it won’t be a threat in coming years. Which gives us another reason to daven for rain.

There is much to learn from the story of the gypsy moth caterpillar about the marvels of Creation, and the limited control of human beings over even the smallest and most fragile among them.