The Backyard Naturalist – The Pest Within

Making Peace With the Eastern Tent Caterpillar

The other day, as I praised gulls, and pigeons, and crows, my friend asked if there weren’t any animal species I disliked, suggesting that surely cockroaches are universally reviled. I said I like cockroaches one on one, but a seething mass of them was indeed unnerving. It brought me to the question of what defines a pest. As spring comes on, insects begin to turn up again, sometimes in exactly the kind of swarming hordes that so often trigger disgust. Tent caterpillars fall into this category. As I began reading about them, I found a recurring phrase: “a forest pest that is native to New England.”

I kept pondering that phrase; something about it niggled. Finally, it occurred to me. That classification commits the logical fallacy known as “begging the question,” a thinking error that presumes an answer and then uses that presumption as evidence of itself. It is, therefore, a form of circular reasoning.

The cognitive dissonance I experienced came from my own understanding of the word pest. For me, it conjures not a particular species, but a certain combination of overabundance and inappropriateness of place. Of course, decisions about when a creature has become too numerous, or where it should and should not be, are not made on objective grounds, but largely on emotional ones.

The animals I was thinking about as I considered this are called eastern tent caterpillars (Malacosoma americanum). These are the ones that sling huge silken hammocks in the forks between tree limbs in spring. Certainly, the caterpillars can munch off almost every leaf on their home tree, but these plants have coevolved with the creatures, and rarely does a tree die or suffer severe consequences from the grazing. These caterpillars are not a pest in an ecological sense. The same articles that refer to the animals as pests also call their web homes “unsightly,” but think how astonishing that claim is — that there is an objective standard across all humanity as to what is aesthetically displeasing and what is beautiful. The articles also point out the unpleasantness of stepping on or driving over the squishy-bodied hordes as they march off their trees, full bellied, in late spring to find a place to pupate and become moths. 

Receiving these descriptions passively, and leaving them unexamined, means to accept the story as written: Grotesque masses of writhing, animate, defoliation machines leave trees  disfigured and vandalized. But there is another story. I have a book called “Guide to Observing Insect Lives.” It’s less an identification-type field guide, telling you how to name the insects you see, and more about approaching whatever you find with curiosity, and with an appreciation for all animal kinds as what writer and naturalist Henry Beston called “other nations.” In this guide to their lives, the authors are almost rhapsodic about eastern tent caterpillars, wondering at behaviors like their tendency to huddle together, especially on cool gray days, or the way they mark their daily travels along the tree’s twigs, unspooling silk behind them so they can find their way home again to the web nest. Other individuals will follow the strands, too, using their thickness to tell them where the richest leaf troves are to be found. This kind of communication and interrelatedness is what we love about honeybees. What is it, then, that we so deplore in tent caterpillars? They congregate, they make a home, they devote part of the day to work, part to eating, part to rest. They are numerous, soft-bodied, social animals. Maybe it’s not their foreignness, their weirdness, but, when we really get down to it, their similarity to us that makes us look away.