Most mammals--including humans--delight in the taste of freshly-picked wild cherries. Such tasty fruits are consumed by everything from 'possums to 'coons to foxes, which promptly absorb sugar from the sweet pulp and later deposit the seeds in their droppings.

Cherry trees also provide food for a number of other animals that don't even eat the fruit. The leaves of cherries, for example, are an ample nutritional source for the Eastern Tent Caterpillar, Malacasoma americana.

In late March throughout the Piedmont, tent caterpillars are one of the first noticeably active insects. Almost overnight, small white bags appear in crotches of cherry trees just as their tender leaves burst from bud. Each bag, looking rather like a dense spider web, is the cooperative effort of silk-spinning larvae of tent caterpillar moths.

During warm days in early spring, up to 300 tiny caterpillars hatch from a shiny, mahogany-colored egg case laid the summer before on a twig. The case, typically found on black cherry, chokecherry, and apple, is a hard foamy material that protects the eggs from winter rains and most potential predators. When the caterpillars hatch out, they are scarcely an eighth of an inch long, and it takes a lot of them to spin the communal web from silk glands near their mouths.

Each caterpillar from a given egg case somehow meets its siblings at a strategic crotch and cooperates in constructing the first small tent. Over the next month or so, the colony may enlarge the residence many times, weaving new tent layers over old as larvae grow larger. The caterpillars molt five times, eventually attaining a length of about two inches, and their old skins and their droppings (called "frass") are buried beneath new tent layers.

The tent caterpillar is typically greenish with two predominate yellow or tan stripes along its length. Toward the head end are the six walking legs characteristic of all insects, but there are also several sets of "prolegs"--thumb-like skin extensions that grasp like legs. With true legs and prolegs, the caterpillar either "flows" along branches or holds tight during windstorms and spring rains.

Tent caterpillars have long hairs that sparsely cover their body. These hairs appear to make the larvae unpalatable to most bird predators, but Yellow-billed Cuckoos and Blue Jays gorge on them. In fact, in some years when there are large numbers of tent caterpillars, there also seem to be bumper crops of cuckoo nestlings.

As a caterpillar colony strips the host tree of its leaves, the larvae may wander in search of another food source, leaving silken trails that lead them back to the tent. During these wanderings many larvae become two-dimensional beneath auto tires and pedestrian shoes, and some are dehydrated by the sun's rays.

Eventually, however, the surviving larvae disband and each seeks out a spot in which to form the pupa, a resting stage that precedes the adult. Usually the caterpillar spins a tough cocoon containing a powdery yellow substance that comes off on contact; the powder is diagnostic for identification of tent caterpillars cocoons. (In my Northwestern classroom, we have observed this species forming pupae without protective cocoons, but this is atypical behavior probably caused by the stress of captivity.)

After spending two months as cocoon-covered pupae, tent caterpillars emerge as adult moths, many of which fly into porch lights and automobile headlights. This summer, look for small tan moths with one-inch wingspans and thin white wing bands; these may be the adults from the tent caterpillar. After the moths mate, females deposit egg cases on suitable cherry twigs, and all adults die. By then, the healthiest trees will have overcome tent caterpillar gluttony by sprouting new buds and leaves.

This year seems to have brought an unusually large number of tent caterpillar webs and greater cherry tree defoliation. A mild winter may have allowed eggs to go undamaged, or perhaps cherry trees provided particularly good nutrients for last year's developing caterpillars. Regardless of the causes of the caterpillar explosion, I'll be watching soon for what may turn out to be a great summer for baby Yellow-billed Cuckoos.

Back to Piedmont Naturalist Volume 1 (1986)