I noticed a few wasps (Polistes exclamans) cruising the milkweed patch during the sunny part of the days since the monarch caterpillars hatched. I know wasps hunt for caterpillars to feed their larvae. But I hoped the monarch caterpillars, being bad tasting, would not fall prey to these wasps. Still it seemed some of the caterpillars had, um, gone missing. The other day a really fat caterpillar, the biggest one, was gone. A wasp kept circling the area beneath the plant where this caterpillar had been, for all the world looking like she had dropped something into the underbrush below. I found the damaged body of a smaller monarch on the ground but never saw any sign of the big one again. Maybe it survived.
Or maybe not. Yes, these wasps do prey upon danaus plexippus. I watched as one of them cut a piece from a medium sized caterpillar and flew off with it, presumably to its nest.