Oak Gall Wasps

When a wasp lays an egg in a leaf bud on an oak tree, it develops into a little, apple-like fruit known as an oak gall. The development of the oak gall is stimulated by a chemical released by the larva. The larva consumes the gall tissue as its food source. It will consume it and the tree's roots before finally developing wings and flying away. Up until the middle of the nineteenth century, the most common ink recipe was an iron and oak galls mixture. The United States Postal Service even had its own official recipe.