7. The Initiation Of Insect Galls The most fascinating galls are sometimes referred to as "controlled galls" because they grow into a specific size, shape and color that is characteristic of a particular species of wasp. Gall formation begins when a female gall wasp injects her eggs into a bud, leaf or stem. Upon hatching from the eggs, the hungry larvae begin feeding on the host tissue surrounding them. The plant's defensive reaction to this intrusive mechanical or chemical irritation is to isolate the toxins or activities of the invader in a tough, tumorous mass of tissue called a gall. Ironically, in doing so the plant provides food and shelter for the developing ravenous larvae. After completing their growth and metamorphosis, often many months later, the adult wasps escape by chewing a circular exit tunnel through the wall of the gall. The precise mechanism by which different species of wasps produce such remarkably unique galls is still being debated by cecidologists (people who study galls).