Harvester: Maryland’ s carnivorous caterpillar
Photos: top: Rick Borchelt; below: walter gould
Top: Striped hairstreak; above; the less common coral hairstreak.
smallest butterflies but also some of the most beautiful. Few are larger than a nickel, and most sport tiny hairlike projections from the back of their wings that give this group its name. It’ s thought that these“ hairs” mimic the antennae on the butterflies’ heads, and indeed if you watch hairstreaks, you may see them rubbing their hindwings together slowly to complete the disguise. The actual antennae of hairstreaks are colored in rings of black and white which serve to break up the silhouette of an antenna and further fool predators. While it was originally assumed that these fake antennae drew the attention of birds, which would strike the fake head at the end of the wings and allow the
Eric Carle’ s Very Hungry Caterpillar eats its way through a bunch of mostly green things: apples, pears, green leaves, plums and a few gastronomically dicey things like chocolate cake, pickles, and even a piece of sausage. This adventurous dining ends up giving the caterpillar a stomach ache until he returns to his vegetarian diet.
You don’ t normally think of the namesake caterpillar as a voracious carnivore, greedily vacuuming up other insects to satisfy its hunger. In Montgomery County, however, we have just such a very hungry caterpillar.
As an adult, the dime-sized harvester butterfly( Feniseca tarquinus) looks and acts like many other Maryland butterflies. The only difference is that, instead of nectar, the butterflies feed on sap, rotting fruit, and the droppings of animals along the wooded trails it prefers. But as a caterpillar, the harvester is a veritable killing machine. Female butterflies search out colonies of woolly aphids, tiny sap-sucking insects that look for all the world like thousands of bits of cotton fluff, especially common on beech and alder. When she finds such a colony, she lays a single egg on a twig in the midst of the aphids. When the egg hatches, the young caterpillar begins its life of carnivory.
Harvester caterpillars are prodigious eaters of an aphid-only diet. This pits them against the dedicated aphid protectors, ants, which shield the aphids from predators in return for the sweet honeydew the caterpillars produce to reward their benefactors. But unlike hairstreaks, harvester caterpillars don’ t produce honeydew to placate ants; they are however masters of camouflage and blend in exquisitely among the aphids. Because their diet is exclusively protein they complete their caterpillar phase quickly, in as little as a week. They crawl off a short distance from the aphid colony and form their chrysalis, where their transformation into an adult butterfly takes place. If it’ s a female, she may even lay eggs in the same colony of aphids that supported her as a caterpillar.
Because their food source is usually present all summer long, harvesters can be found in the Reserve all through the warm months, but especially in summer. Look for them along wooded trails, especially near streams, and check out any aphid colonies you find for“ bumps” along the twig that will be the nearly mature caterpillars.
As North America’ s only carnivorous butterfly, harvesters are a unique part of the Ag Reserve’ s butterfly fauna.
Photos: Bonnie Ott
As a caterpillar, the harvester’ s coloring lets it lurk among the woolly aphids it eats. As an adult butterfly, its coloring blends in with the sun-dappled forest floor.
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