bugguide. It turns out that they are bees! There is such a thing as a metallic green bee.
Of course, now I want to know what the difference is between bees and wasps. If you'd asked me before, I'd probably have said that bees are chunky, fuzzy creatures and wasps are sleek, non-fuzzy creatures. But that, clearly, is not the difference. And, since some bees are solitary and some wasps are social, their lifestyle doesn't help much either. Anyone got any ideas? Information? Links?