Last fall I found the ootheca of what I think was a carolina mantis and decided to keep it until the eggs hatched. Although a few little mantids did hatch, most of the eggs had been parasitized and the container I had the ootheca in was full of these tiny hymenopterans. They were about 2mm long (not including the females' ovipositers), metallic green with red eyes, and they had thick "thighs" on their third pairs of legs. I think they might be chalcid wasps, but I'm not sure.
Here's the female: