Predatory and parasitic wasps

To butterfly enthusiasts, wasps are the vespa non grata of the insect world.  The first problems arise from predatory wasps - the kind that pick up caterpillars whole and carry them off.  I had a frustrating summer trying to raise Cabbage Whites on Brassica plants, even up on a balcony away from ants and slugs.  Eggs would appear, then small caterpillars, then bigger ones, then... gone.  They weren't wandering - they were being abducted, presumably by wasps carrying them off to burrows (although I never saw the malefactors, so it's possible that birds or other predators may have been responsible).

To cope with predators of that sort, the cheapest response is to wrap the host plant in tulle - the same fabric used for wedding decorations.  Shown above is tulle covering a flat of milkweed and wrapped over a pot of cabbage.

A much more difficult problem arises when dealing with parasitic wasps.  I posted a gruesome but utterly fascinating video back in January, showing the larvae of parasitic wasps bursting out of the body of a caterpillar, whose brain has been hijacked as well, so that it spins a protective cocoon over the emerged larvae.  And a little over a year ago I posted two photos of the remarkable Ichneumon wasp (click on the lower of those two pix to see her magnificent ovipositors).

I had originally thought that the tulle wrapping of the host plants would keep out the parasitic wasps (it would certainly exclude an adult Ichneumon wasp).   I was therefore somewhat dismayed to see Ed Yong's report earlier this year about the sensory skills of Trichogramma wasps.  The part about anti-aphrodisiacs was interesting, but what opened my eyes was this photo -

- showing the parasitic wasp to be smaller than the eyeball of the butterfly.  I don't think my tulle (or my more recently-acquired paint-straining fabric) has any chance against that little bugger.

The other photo at Ed's article shows that the wasps are smaller than the butterfly's eggs, and that's part of the problem, because even when I bring butterfly eggs in to an enclosure to raise them, it's possible that they were parasitized even before they hatch.  More about that later when I show the havoc wrought by parasitic flies on immature Red Admirals.