Macro Monday: Hornworms' Lament

“Fish gotta swim and birds gotta fly. Insects, it seems, gotta do one horrible thing after another.”

-- Annie Dillard, Pilgrim at Tinker Creek

Our friend Andy spotted these two critters on the currant tomato that is growing rampantly in the washtub by the grape arbor.






They are larvae of Manduca quinquemaculata -- the five-spotted hawk moth -- aka tomato hornworms.

And they have munched their last nightshade leaves.

The stuff that looks like a a threadbare white shag carpet are parasitoids -- the pupae of a braconid wasp. As larvae, they already ate most of the insides of the hornworms, which maintain just enough life to cling to the branch where they stopped. (I took these photos on Saturday, and the worms are still where we left them.) Soon they will hatch out into adults and go hunting other hornworms on which to lay their eggs. I've never seen a hornworm with this heavy a parasitoid infestation. I guess they aren't any more doomed / dead than one with a few pupae.

I'm ambivalent about this particular horrible thing. The hornworms can really play hell with the tomatoes, and the little wasps are very effective at controlling them. But the adult moths are magnificent -- easy to mistake for hummingbirds when one first sees one -- and we have lots of tomato foliage. When I find a healthy hornworm, I tend to just stick it on a robust volunteer tomato somewhere away from the garden, or else on some wild nightshade.

The life cycle of parasitic wasps is the stuff of nightmares and the inspiration for some viscerally horrifying speculative fiction.

Detail