Last spring (2010) I got to watch a mason wasp, Ancistrocerus waldenii, building a mud nest by my parents’ back door. I was standing there with my nieces one morning, while the nest was still in construction, when one of them spotted a bright green wasp nearby. I told them that it was a cuckoo wasp, which (as you might guess from the name) lays its eggs in the nests of other wasps. Right on cue, it flew over to the open mason wasp nest and disappeared inside.
Two months later, I spent a couple of weeks house sitting for some friends, and there was a similar mason wasp nest by their front door. I was checking on it every day in the hope that I would get to see the wasps (or their parasites) emerge. At one point I had to leave town for a wedding, and when I came back the next morning there were six exit holes–I had missed it.
Early this past summer my friends reported that the holes were all filled in–they were being reused by other mason wasps, or maybe by keyhole wasps, spider wasps, or mason bees. When Noah (Charney, my coauthor and our mutual friend) was at their house for dinner one evening, he attached a plastic bag around the nest to capture whatever emerged. This worked, and he was able to get pictures of the first wasp that emerged before letting it go. I never saw the pictures, and am only remembering this now because in going through my own photos from this past July, I just came to this one:
I wish Noah had reattached the plastic bag, because clearly more than one kind of wasp ended up emerging: three mason wasp-sized wasps, and three smaller ones that evidently parasitized the other mason wasp-sized wasps. In addition to wondering what they all were, I’m wondering what the deal is with the leftmost little hole, which corresponds with a discolored spot in the photo from the previous year. I’m thinking that maybe there were seven original mason wasp larvae and that one of them was parasitized, the parasite producing an exit hole that had already been appropriated by some other little mud wasp by the time the other six emerged as adults. Oh well. Maybe next year I’ll happen to stop by at the right time to see some of the comings and goings from that nest. So much going on in such a nondescript blob of mud.
Added 4/14/2012: Apparently I had seen Noah’s photos and had forgotten about them. I just got an email notification that the wasp had been identified as Ancistrocerus waldenii. So this is likely a case of an A. waldenii nest being reused by A. waldenii.