Each cocoon was only 4 mm long. Wouldn't that be too small for a wasp? Perhaps these could have belonged to some sort of fly? They look like a picture of a sawfly cocoon that I saw but that cocoon was not in a group like these.

Parasitic wasps, especially chalcids and many braconids are not classed as "micro-Hymenoptera" for nothing. In fact, "fairy flies", are the tiniest of all insects. These cocoons are almost gigantic at four millimeters, and very typical for braconids.

Thanks for the feedback! I'm so very new at this that I didn't even know about the Family Braconidae and how small these wasps can be. 1 mm. Amazing. Up until now, whenever I've thought of wasps, I've always thought of the big ones that chase people when you get around their nest. I didn't know about these little ones. Very interesting. BugGuide sure has been an eye-opener for me! :)