FROM THE GROUND UP: The upside of tent caterpillars

A silky nest of the Eastern Tent Caterpillar.
A silky nest of the Eastern Tent Caterpillar. PHOTO BY PAMELA BAXTER

Right now, they’re everywhere — those white, webby, Halloween-y things in the crotches of tree branches. Inside the webs are hundreds of wriggly, leaf-chomping Eastern Tent Caterpillars. Ick.

Not so long ago, first thing in the morning while the larvae were still in their nests, I would go out and squish them with my gloved hands. Lately, I’ve just let the caterpillars do their own thing; I can’t bring myself to kill them anymore. This doesn’t mean that I have come to love these creatures; only that I seem to have become more squeamish over the years. Also, I’ve observed that not every year is a devastating one for the tent caterpillars’ favorite food trees: cherry, apple, peach, plum, hawthorn, and other members of the Rose family (Rosaceae).

But I recently came across an article that made me realize that I had fallen prey to a common stereotype: creepy, tree-defoliating caterpillars are all bad. Could there be a positive side to this unsightly, destructive pest? It turns out that there is: these caterpillars emerge at just the time that the spring’s new crop of baby birds needs to be fed.

Thanks to Sarah T. Bois, Ph.D., writing for the Nantucket Chronicle on May 18, 2015, I’ve updated my thinking on these leaf-eating pests. In her article, “Got Tent Caterpillars?” Bois, who is the Director of Research and Education at the Linda Loring Nature Foundation in Nantucket, Massachusetts, asked, “Do you feed the birds? Have a bird bath? Well, you are getting bountiful supply of protein free from Mother Nature.” http://bit.ly/2rdJ4fJ

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Caterpillars are highly nutritious and make easy pickings for birds. Finding a batch of tent caterpillars must be the equivalent of a bird walking into a deli. In fact, according to research conducted at the Minnesota Agricultural Experiment Station, sixty species of birds feed on Eastern Tent Caterpillars. These include many of the birds in our area, including bluebirds, mockingbirds, orioles, chickadees, blue jays, grosbeaks, waxwings, robins, and cardinals.

This same study also found that “tent caterpillar outbreaks are controlled by native predators and parasites including 127 insect parasites, 28 insect predators, frogs, mice, bats, reptiles, squirrels, skunks, and bears. By sifting through one day’s worth of bear poop . . . researchers found that a single bear on average ate around 25,000 caterpillars in a one day” (“Tent Caterpillars are for the Birds,” by Kay Charter Eric Ellis, June 28, 2011, https://www.rivercare.org/news/tent-caterpillars-are-for-the-birds)

In her article, Bois goes on to point out that “healthy deciduous trees usually survive defoliation and grow back a second set of leaves by July.” And rarely are trees fully defoliated. “Eastern tent caterpillars go through regular boom and bust cycles . . . Populations of tent caterpillars reaching highly noticeable levels run approximately on 10-year cycles and usually last 2-3 years,” she says.

If nothing else, the story of the tent caterpillar is a reminder of the importance of observing nature before taking action. Often, what we do without understanding a pest creature’s place in the web of life has negative effects on other species. As Charter and Ellis note in their article, “What people find unsightly and annoying for a few months some years is a welcome gift of easy food for many species of wildlife and the species that in turn feed on them.” In the case of tent caterpillars at least, you can take a laissez-faire attitude and feel good about it!

Tip: For easy removal of the unsightly webs when the caterpillars are finished with them, tie or tape an old T-shirt or rag onto the end of a broomstick. Swipe/rub this against the silky nests with a twisting motion, and the nests should stick to the fabric.

Pam Baxter is an avid organic vegetable gardener who lives in Kimberton. Direct e-mail to pamelacbaxter@gmail.com, or send mail to P.O. Box 80, Kimberton, PA 19442. Join the conversation at “Chester County Roots,” a Facebook page for gardeners in the Delaware Valley. Go to Facebook, search for Chester County Roots, and “like” the page. To receive notice of updates, click or hover on “Liked” to set your preferences.