Ever since I made a place on BugGuide to collect photos of them over a decade ago, I’ve been wanting to see (in person) one of those weird wingless gall wasps that can be found throughout the winter. Two years ago I put them on the “winter bug bingo” card I made for the online “Bugs in Winter” course I put together, and I think one participant managed to find one, but I wasn’t so lucky.
Last fall at the end of a game of tennis, I noticed a white oak leaf at the edge of the court with a couple of “oak pea galls” on it, like this one:
This gall is caused by Acraspis pezomachoides (Cynipidae), and knowing that Acraspis is one of the genera with wingless adults, I decided it was time to be a little more proactive in my quest to see one, so I took the leaf home and stuck it in a jar. But alas, I just got a couple of lousy parasitoids.
Last month, while leading a workshop on identifying invertebrate tracks and sign, I picked up a white oak leaf with an “oak hedgehog gall” on it—made by the related species Acraspis erinacei. It was already brown like the one pictured above, but here’s what a fresh one looks like:
I decided to try again, so after everyone had gotten a good look at the gall, I had Julia put it in her backpack.
A week or so ago, I remembered the gall and had Julia fish it out of her backpack. I put it in a vial on a shelf in my office, and every couple of days I’ve remembered to check the vial (most of my other bugs having been put away for the winter at this point).
Last night I checked, and there she was!
Here’s what the gall looked like after she emerged (the exit hole is at the bottom, near where it’s attached to the leaf).
The adults that emerge from round, faceted galls like this—provided that they are not parasitoids or inquilines—are all wingless females. Like most cynipids, Acraspis species have a two-part life cycle. These females climb up to white oak leaf and flower buds and lay eggs in them. Tiny, inconspicuous galls form in the buds (see examples at gallformers.org), and winged males and females emerge from these in the spring. After mating, females lay eggs in midribs of white oak leaves, and the galls that will produce the next set of wingless females develop over the summer.
Virtually all of the bugs I raise are unknowns that have to be killed and preserved to be identified, so it was nice, for a change, to raise one that already has a name and whose whole life cycle has already been worked out. This morning I took her out to a white oak sapling in the woods behind my house and set her on it, thinking maybe I’d get to see her lay some eggs.
No such luck; she didn’t seem to like this sapling, and started making her way down its stem. So I moved her to the trunk of the white oak tree that was right next to it. There, she decided to just sit and preen for a long, long time.
It was below freezing out and my fingers were getting cold, so I decided to leave her to it.
When I stopped to feed the chickens on my way in, I found another wingless weirdo waiting for me by the door of the shed: a female fall cankerworm moth (Geometridae: Alsophila pometaria). ‘Tis the season, I guess! Her eggs will overwinter, hatching in the spring into inchworms that will nibble the leaves of the apple or cherry tree overhead, from whence she presumably came.
Oh, and tonight I checked the vial with the gall again and discovered that another Acraspis erinacei female has emerged. As noted on gallformers.org (which I highly recommend for identifying galls and reading up on what’s known about them), these galls may contain between two and eight central cells with individuals of A. erinacei (or their parasitoids) developing in them, as well as additional cells around the periphery with inquilines developing in them. Inquilines are (in this case) cynipid wasps that develop inside the galls induced by other cynipid wasps, without (necessarily) killing the original inhabitants. Twelve winters ago, before I knew anything about the life cycle of Acraspis species, I collected some A. pezomachoides galls from under a white oak tree, assuming that what emerged would be Acraspis adults, but instead I got nothing but inquilines, which emerged in early June—thereby skipping the alternate, bud gall-inducing generation of their host species, and appearing just in time to find some developing “pea” galls to lay eggs in. This one’s a male: