Wild Ideas: Convenience stores in the trees   

Eastern tent caterpillars, like the ones above, prefer to build their tent-like nests in black cherry and other trees in the rose family. Pam Owen | Rappahannock News
Eastern tent caterpillars, like the ones above, prefer to build their tent-like nests in black cherry and other trees in the rose family.

If I’ve learned nothing else from nature, it’s that all our native species are important, no matter whether we humans like them or not. Last week I saw a good example of how one less-loved species benefits others that we tend to love more.

One morning I was engaged with one of my favorite activities — sitting on my deck, drinking coffee and listening to birds singing in the forest all around me. As I scanned the tops of the tall trees across my driveway to see what might be singing there, I caught a flash of color. I could barely make out a bird, about the size of a robin, through the little foliage left on a nearly denuded black cherry tree (Prunus serotina).

Grabbing my binoculars, I moved to where I could get a clearer look. The bird was orange, with dark wings, so I knew it could only be a Baltimore oriole. The other oriole native to our area, the orchard oriole, is smaller, about the size of a warbler. The orange was not as bright as I had first thought, and the dark wings were more grey than black (with yellow and white bars). This bird also did not have a black hood but instead just a bit of gray stippling mixed into the orange, indicating this was a female, not the flashier male.

The male Baltimore oriole is hard to miss, with its bright-orange body contrasting with its black hood and back, and black-and-white wings. Andy Reago & Chrissy McClarren via Wikimedia
The male Baltimore oriole is hard to miss, with its bright-orange body contrasting with its black hood and back, and black-and-white wings.

The oriole was busily dragging tent caterpillars out of the nest they’d made in the tree, banging them against a branch, then wolfing them down. Once available, fruit makes up the bulk of the Baltimore oriole’s diet, but this time of year insects, especially caterpillars, provide much-needed protein for adult orioles during the breeding season and, a bit later in the spring, for their young.

The following day I spotted a female American goldfinch working a tent caterpillar nest on another black cherry tree, almost as denuded as the one the oriole had been hunting in. Insects also make up a small but important part of the goldfinch’s diet, which mostly consists of seed. Having so many high-protein snacks in one place makes the tent-caterpillar nests a virtual convenience store for the goldfinch, and a fast-food restaurant along the migratory highway for the oriole.

Eastern tent caterpillars (Malacosoma americanum), which are common in our area, live communally in a silken tent-like structure the larvae weave around the nodes of tree branches when the larvae are about two inches long. This species of tent caterpillar usually sticks to one tent, while others in the genus keep moving, building a series of small tents as they go along. Webworm caterpillars also create web-like shelters out of silk, but enclose small branches and leaves at the ends of the limbs rather than building their shelter between limbs.

As with many species, the female Baltimore oriole is much drabber than the male.David Menke, U.S. Fish & Wildlife Service
As with many species, the female Baltimore oriole is much drabber than the male.

Eastern tent caterpillars leave during the day to feed, but return to the nest at night, or during rainy weather, according to the Virginia Cooperative Extension’s publication “Eastern Tent Caterpillar,” on VCE’s publication website. Wherever the caterpillars go, they keep secreting silk and pheromones, leaving a trail that guides their ramblings. 

These caterpillars seem to be having a good year; their tents are everywhere in black cherry trees and other members of the rose family (Rosaceae), their favorite hosts. Every eight to 10 years, they will boom for a couple of years, then bust. While predation helps to keep their populations down, disease or shortage of foliage on the host trees are bigger factors. The tent caterpillars that survive hatch out into little furry, brown moths.

Sometimes tent caterpillars go walkabout, moving on to other food sources. I’m finding more and more crawling on my house every day now, several yards from any nest. Perhaps they’re leaving nests disrupted by predators, or just leaving trees they’ve denuded to look for other food. Although host trees seem to take a hard hit from the caterpillars, within a few weeks after the larvae leave, the trees usually snap back, leafing out again. Our having to look at some bare branches seems like a small price to pay to keep the convenience store open.

© 2015 Pam Owen

More about tent caterpillars, orioles . . . and free trees

Managing tent caterpillars: While eastern tent caterpillars provide important food to many native animal species, they can be a problem when they infest a specimen tree in someone’s yard or invade orchard crops. Other than black cherry, the caterpillars favor chokecherry (Prunus Virginia, also in the rose family) and apple but will also feed on hawthorn, pear, plum and flowering fruits. VCE has several publications available on its website about the life history and how to manage infestations, or contact your local Extension agent for more information.

Free trees: The Culpeper Soil and Water Conservation District announced last week that it is giving away 1-year-old seedlings to local citizens. Species vary, and the trees are being given out on a first-come, first-served basis. The trees are made possible through a partnership between the Vaughn Bassett Furniture Company, in Galax, and the Virginia Department of Forestry. For every tree the company uses in the production of their furniture, the furniture company donates one tree to VDOF, which uses the trees for various planting projects. To pick up a tree, come to the CSWCD between 8 and 4:30 weekdays. For more information, contact Stephanie DeNicola at stephanied@culpeperswcd.org or 540-825-8591.

The remarkable nests of orioles: The female Baltimore oriole weaves a distinctive sock-like nest in several species of trees, preferring elm, maple, willow, cottonwood and apple. The nest is hung by its rim from branches, sometimes the trunk, and is intricately woven from plant fibers (including milkweed), hair, grapevine bark and even string and yarn. You can attract these beautiful birds to your yard by putting out a commercially available nectar feeder that is similar to that used for hummingbirds but built to handle the larger oriole. The magazine “Birds and Blooms” has an excellent article about other ways you can attract orioles. Male Baltimore orioles have a beautiful song; the female also sings, mostly in response to the male.  

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