Wasp-eating moth fills rare niche

Sooty-winged Chalcoela moth/Jim McCormac/For the Dispatch

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Columbus Dispatch

February 19, 2017

NATURE

Jim McCormac

One August evening last summer, I was in Adams County in southern Ohio shining specialized lights on white sheets with some expert lepidopterists.

We were trapping moths deep in the midst of the Nature Conservancy's Edge of Appalachia Nature Preserve, which encompasses 20,000 acres. "The Edge" harbors some of the richest biodiversity in the Midwest.

Like a moth to a flame, the insects flocked to our sheet. We could survey what was present without needing to kill or collect the specimens.

At one point, a moth unknown to me fluttered in. It was gorgeous: tawny-buff in color, with large patches of peppered black and white. Gemlike dots trimmed the trailing edge of the hind wings.

We had lured a sooty-winged chalcoela, or Chalcoela iphitalis.

Someone mentioned that it is a parasite that kills paper wasps.

"What?" I exclaimed. "You've got to be kidding!"

Nearly everyone knows paper wasps, in the genus Polistes. They construct many-chambered, papery nests that hang from slender stems under the eaves of buildings and other structures. The adult wasps fiercely protect their nests and a female's sting packs a punch.

Sure enough, sooty-winged chalcoela caterpillars consume the larvae of various paper wasps. This is rare. The vast majority of caterpillars, the larvae of moths and butterflies, are strictly vegan.

Soon after my initiation to this bizarre moth, an acquaintance showed me a photo of a moth that mystified her. It turned out to be a sooty-winged chalcoela, resting on the side of her house only inches from an active paper-wasp nest.

Figuring that the moth had raided the wasp's lair, we hatched plans to inspect the nest once winter set in and the wasps were gone. On the frosty night of Dec. 23, we removed the wasp nest from the eaves and took it inside for inspection.

It didn't take long to find the tiny moth caterpillars. The nest was infested with a dozen or more.

Each of the cells within a paper wasp nest contains a wasp larva, or grub. The female chalcoela moth flies to the nest under cover of darkness, when the wasps are inactive, and lays eggs on the structure. Caterpillars soon hatch, invade the cells and consume the wasp grubs.

By the onset of winter, the caterpillars are ensconced within dense silken cocoons woven within the cells, or on the back of the wasp nest. Come summer, the adult moths will emerge and begin the cycle anew.

As adult paper wasps often hunt and feed on moth caterpillars, this is a particularly apropos form of revenge.

Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.

An active paper wasp nest, fiercely guarded by its inhabitants. This is the actual nest that was parasitized by the moth in the accompanying images.

A sooty-winged chalcoela caterpillar peeks from a cell in the wasp nest.

A closer view of the caterpillar. This is its head, and the foremost three pairs of legs (thoracic prolegs)

A caterpillar, removed for inspection. It is the spitting image of the wasp grubs that it consumes; maybe visual trickery plays a role in protecting it from wasps.