Carnivorous caterpillars? In my aphid colony? It’s more likely than you think.

If you’re a beech blight aphid (take our quiz here here to find out), you’d best run while you can! North America’s only carnivorous butterfly caterpillar is on the loose, and on the menu? You.

The harvester is an energetic flyer as an adult, feeding on sap, dung, and mud (as opposed to nectaring on flowers), but the larva is a little different; it is slow but steady, certain death.

Something so sinister shouldn’t look so cute and fuzzy, but the harvester caterpillars are just that – mostly white and hairy, which helps them seamlessly blend in to the aphid colony they haunt. In some cases, they even attach the discarded carcasses of their aphid prey to themselves with silk, making themselves the invertebrate version of wolf in sheep’s clothing!

The aphids themselves feed on the sap from their host tree, and the liquid they excrete, honeydew, is a delicacy among insects. Ants, wasps, flies, and other invertebrates (including the adult harvester!) feed on the sweet substance. Some, such as the ants, will even defend the aphids to ensure their continued access. This honeydew also drips down onto the host’s branches and ground, where a fungus, sooty mold, grows – yellow while actively growing during summer and black in the winter.

After the harvester caterpillars have spent a week feeding and growing on their strictly meat diet, they will have gone through four instars and are ready to pupate.

It was actually this pupa (below) that I found first, before spotting the caterpillars of a second brood (above) about a month later.

When the adult butterfly ecloses the following spring, the carnage will continue.

– Naturalist Leah