Oh, how interesting. You have a great example of biological control in action!

This is a relatively common phenomenon in which a predator insect hollows out the soft pithy center of a stem in order to lay its eggs.

Do you see the tan "plug" at the far left and another towards the right? That's evidence of a small predator wasp which is stocking each cell (the space between 2 plugs/partitions) for its youngsters. The prey are alive, but stunned, and will provide fresh "food" for the predator's young.

One cell per youngster. Many prey per youngster; with more prey for females than for males.

I'm curious where you live. Please tell us city & state.

I was thinking it looked as though these flies were being stocked up by some other creature. Ok I am off to look up more info about wasps doing this. I live in Iowa. Thanks for the reply!

Fascinating, jean! This one really had me scratching my head. The image was perplexing, to me. Any idea what genus of wasp this might be?

No I don't.
And I would like to know if the prey truly are flies. I can't see enough detail to be certain.

Okay, this is the back story. I have a friend who is a fanatic about monitoring & documenting mason bees in the local Master Gardener demo garden.

And since he started, he has seen several predatory wasps also using his bee nests.

If you're interested, reserch these:
- Isodontia elegans, common name the grass-carrying wasp -- a wasp about an inch long; prey are tree crickets
- Passaloecus species -- a very small predatory wasp; prey are aphids

This post was edited by jean001a on Tue, Jul 1, 14 at 17:25

Here is a photo of one of the insects in the stem. Has fly shaped wings and eyes as far as I can tell.

I am only seeing signs of activity in my cut peony stems. So fascinating! I haven't spotted the creatures doing this though.

I think you're correct. Can't see antennae but can discern the shape of the head.

Thanks to folks like Jean (and rhizo, for that matter), I never stop learning. That's a new one for me.

tj