Parasitism

       Some of the intruding insects that come from oak galls are not harmless. They are the ones called parasites. They live in the houses not for the sake of the protection or the food furnished by the house, but in order to eat the actual dwellers in the house. Often and often not a single real gall-insect comes out in the spring from many of the little houses, but only a little swarm, or sometimes just two or three, or even one, of these insect-devouring parasites that has eaten up the rightful owners of the house. Vernon L. Kellogg, "Insect Stories."