Galls are not unique to Creosote. In-fact they are quite common, especially among oak species. Gall wasps actually specialize in forming galls, most often on oak leaves. Gall formation almost always is part of the reproductive life cycle of these wasps. There are well over 1000 species of Gall Wasps, each individual species specializing in forming galls on one specific plant species. These galls are often quite unusual looking, sometimes looking even Christmas ornament like. Below are a few pictures of galls.