Oak Galls

Oak Rough Bulletgalls are produced under the direction of the tiny gall wasp. The “rough” in the common name refers to the roughened appearance created by tiny hairs covering the surface. The sturdy galls can be round like a musket ball or slightly elongated like a Minie ball, which accounts for the “bullet” part of their common name.

Small, round, fuzzy wasp galls on the underside of distorted leaves can draw the attention of concerned tree owners. The galls are produced under the direction of a tiny gall wasp (family Cynipidae) with a big scientific name, Neuroterus quercusverrucarum (syn. N. floccosus).

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.

Rough Oak Bulletgalls induced by the gall-wasp, Disholcaspis quercusmamma (family Cynipidae) are splitting through the bark and rising on the stems of oaks in the white oak group in southwest Ohio. The galls are most commonly found on bur (Quercus macrocarpa), white oak (Q. alba), and swamp white oak (Q. bicolor).

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.

The emergence of the "horns" that give horned oak galls their common name is a short-lived event. I've commonly observed fully extended horns, but seeing them in the process of breaking through the gall surface is a rare treat and it's happening right now in southwest Ohio.