Oak Galls

White, rounded, woolly-looking galls are appearing on oaks throughout Ohio. They are the Wool Sower Gall and are produced under the direction of the gall wasp, Callirhytis seminator (family Cynipidae).

This is the 5th BYGL Alert this season dedicated to wasp galls on oaks. That may seem excessive, but it’s estimated that around 800 types of galls may be found on oaks in the Nearctic which is the part of the world that includes all of the U.S. and parts of Mexico and Canada.

Last week, I came across a burr oak (Quercus macrocarpa) in a southwest Ohio city park with leaves on the lower part of the canopy dramatically embellished with a type of “saucer gall.” The galls were the handiwork of the gall wasp, Neuroterus tantulus (“Gall-Wasp” family Cynipidae).

One of the most unusual galls found on oaks is the light green, ball-like Roly-Poly Galls produced under the direction of the gall wasp, Dryocosmus quercuspalustris (family Cynipidae). The specific epithet reveals one of the most common hosts of this gall-making wasp: Quercus palustris is the scientific name for Swamp Spanish Oak (a.k.a. Pin Oak) with palustris being Latin for “swampy” or “marshy.”

Rough oak bulletgalls are rising from oak stems in Ohio accompanied by their entourage of bodyguards. The galls are found on oaks in the white oak group with burr (Quercus macrocarpa) and swamp white oak (Q. bicolor) most commonly affected. The "mature" galls are commonly covered in black sooty mold.

Dave Shetlar (Professor Emeritus, OSU Entomology) and I have recently observed newly developing oak rough bulletgalls in central and southwest Ohio, respectively. The galls are produced under the direction of the gall wasp Disholcaspis quercusmamma (family Cynipidae). We're also starting to see the gall's security detail, but more about that later.

A couple of weeks ago, me and several of my Extension colleagues came across so-called marginal leaf fold galls on an oak on the OSU campus during a photography workshop. Since that time, I'm commonly finding these galls on oaks belonging to the "red oak group" as well as a similar gall on black locust in southwest Ohio.

I'm always amazed at how the population densities of certain gall-making wasps on oak seem to synchronize over wide geographical areas so that large numbers of the same gall appears over a wide region.  I don't know how they do it.  These are very tiny insects and they have an intimate relationship with their host trees; it's best for them not to stray too far. 

 

Oak button galls on white oak are very common this season throughout southwest Ohio; I even spotted some on oaks in central Indiana.  The galls are produced by the gall wasp, Neuroterus umbilicatus (...