Then, this morning, my sons noticed that our two datura plants (called 'Moonflowers' here by many native Kentuckians: I got these at Hettmansperger Greenhouse) had four worms that were covered with white eggs. Thankfully, they asked me first before squishing them (or throwing them at each other, which is more apt).
The worms were on the underleaf side of the two datura plants (which must be an attractant, like the tomato plants). I decided to clip the leaves and put each one in the shade of some of my potted tomato plants across the way. We'll see what happens. If I find any more without wasps on them they will be plucked off and fed to my free-range chickens.
It just goes to show you that, if left alone, nature often takes care of things quite nicely.