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| Zopheroteras guttatum with a ballpoint pen |
Collecting pin oak,
Quercus palustris, leaves for a school project, I felt a tiny hard bump on one. Under magnification it was a perfectly spherical 2mm gall that looked like a piece of candy. The usual sources couldn't identify it, but I got a rapid response from a submission to
Bugguide. This is a gall of a cynipid wasp,
Zopheroteras guttatum.
Galls catch our eye with lots of pictures but the insects that build them get little respect. In this case I did come up with pictures of a
Z. guttatum adult from the Smithsonian on
Eol.org. Three pages of Google searches yielded only other photographs of galls, most of which were confirmed by Charley Eisman, the guru of galls.
Eisman's describes Z. guttatum galls in more detail. "Causes spherical, 1.45-2.5 mm galls, with purple spots, single on a secondary vein on underside of
Quercus palustris, imbricaria,
or
texana leaf, in fall." Initial descriptions
specified the underside of the leaf but there are
now other examples of the same galls on the
upper side.
I went back to the tree looking for more of these galls but found only other leaf galls. These fuzzy oak leaf galls are far more common, produced by
Callirhytis furva, They are said to drop from the leaves in October but I more commonly find them attached to a fallen dried leaf on the ground. Again, EOL provided a photo of the cynipid wasp that makes the gall.
I haven't had any success in raising the wasp from a gall but I may have given up too soon. Weld who wrote the book says they emerge "in the second or third spring in late March." Typically a cynipid wasp would mate and then lay eggs on a leaf, in these cases a red oak. The mere fact that these 2-3mm wasps would find each other to mate after a 3 year gestation is hard to fathom but "love finds a way,"
Like the
spiny oak galls
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| Hard dried galls - REK |
we wrote about in the past, the hatchling that emerges from the egg creates damage on the leaf which responds by growing around it, creating a shelter and food source until it is ready to emerge. What I find fascinating is the many different ways that the leaf responds, each distinctive for the specific species. I found a few other less distinctive galls on Cyrus's pin oak, including one below that had delivered its young.
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| Empty gall - REK |
Each of these galls are now in clear plastic boxes, trying my wife's patience as they fill the closet. I know she will be excited to know that I now need to keep them for three years.
I went back to the tree looking for more of these galls but found only other leaf galls. These fuzzy oak leaf galls are far more common, produced by Callirhytis furva, They are said to drop from the leaves in October but I more commonly find them attached to a fallen dried leaf on the ground. Again, EOL provided a photo of the cynipid wasp that makes the gall.
