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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Parasitoids at the porch light: Ichneumon wasps, Ophionine


On warm nights in late winter and early spring ophionine wasps are regular visitors to my porchlight.


Last week’s chill left us with a reminder that the ides of March are not only treacherous for Caesars but also for early blooming plants in the mid-Atlantic region. However, just before winter’s last gasp, on a warm evening that accompanied a 70 degree day, I had the pleasure of entertaining a couple of delightful parasitic wasps in the subfamily of Hymenoptera known as the Ophioninae. Each year I welcome these nocturnal visitors to my porch light as one of the harbingers of spring. They regularly appear on the first 60-ish degree evenings in March.


Beneath the glow of my porchlight an ophionine wasp grooms its antenna and then taps its front foot in time with the music.

Ophionine wasps belong to a large and important family of membrane-winged insects known as ichneumon wasps. Ichneumon wasps perform the important ecosystem service of biological control by parasitizing some of our most important pests including corn earworms and white grubs. However, they also attack other non-pestiferous insects including the larvae of butterflies. Some years ago we collected a beautiful caterpillar, the larva of the tiger swallowtail butterfly. After eating leaves like a ravenous teenager, it formed a remarkable chrysalis resembling a dead leaf. We placed the chrysalis in a terrarium and anxiously awaited the appearance of a beautiful swallowtail butterfly. Events took an unexpected turn when a feisty looking wasp emerged from the chrysalis instead of a gorgeous butterfly. You see, unbeknownst to us, prior to our capture of the swallowtail larva, it had been visited by a parasitic ichneumon wasp. The female ichneumon wasp likely grappled with the caterpillar before stinging it and depositing an egg within.

A beautiful ichneumonid wasp rests on the chrysalis of a swallowtail butterfly from which it emerged.

The fascinating part of this story is that the parasite inside the swallowtail did not immediately develop and emerge from the caterpillar. This clever parasite waited for the caterpillar to feed and grow before beginning its own development. The tiny invader then completed its development and emerged as an elegant ichneumon wasp. Parasitoids with this type of delayed development within a host are called koinobionts. Many species of koinobionts synchronize development with that of their host by responding to changing levels of hormones produced by their host during growth and development.

Returning now to the present, if you would like to see other ichneumonid parasitoids, switch on your porchlight on a warm spring evening, and see who arrives. Don’t be surprised if several pale orange ophionine ichneumons appear. If you dare, do as we do and invite them in for a drink. As you see in the video, a little honey and water seemed just the right tonic for these busy parasitoids. After they had their fill, we bid them adieu, and returned them to the wild. Perhaps our hospitality will be rewarded in a few weeks by these ichneumons in the form of koinobionic attacks on the pesky caterpillars and white grubs that perennially plague my flower beds.    


Ichneumonid wasps can be a little testy when sharing a droplet of honey.


The fine references “The Insects: an outline of entomology” by P.J. Gullen and P.S. Cranston, and “Subfamily OPHIONINAE” by I. D. Gauld and D. B. Wahl, were used as references for this Bug of the Week.