The oaks have my attention of late. I’ve been seeing these little growths on the stems of the white oaks and they are not acorns. This one is about 5/8″ in diameter.
Photo taken indoors after the gall was picked during a walk in the rain; mid-afternoon, mid-30’s, March 6, 2013
This is one of a variety of oak galls. Traditionally, they have been used in tanning, dying, and making ink. To get the dark color, iron (ferrous sulfate) is added to the tannin rich solution made from the gall. Oak galls have, also, been used medicinally, particularly, as a powerful astringent. That’s great but what IS a gall you might ask. The diversity of galls is great. Galls seem to be and grow everywhere…leaf, stem, root and initiated by many things…insects, mites, fungi. These galls are formed by a gall wasp and, to no surprise, there are many kinds of gall wasps. Basically, the wasp lays an egg in the tissue of the host plant or tree. This induces the tree to form the woody covering around the growing larvae. The larvae is protected by this shelter and may even obtain nutrients secreted by the gall itself. It is not known exactly what triggers the oak to do this but some theories involve mechanical, chemical, and viral triggers. This gall is old and no longer a living part of the tree. Apparently, the gall dies about a month before the wasp emerges in December-January. Some galls, themselves, are parasitized by other wasps which feed on the larvae. For the most part, the galls do no significant damage to the oak.