The mystery of gall formation was not understood until recent times, even though galls have been written about since the days of the Roman Empire. Thousands of species of insects and mites produce galls on hundreds of species of plants. Each gall-maker attacks specific tissues on a specific plant. The resulting distortion is a distinctive gall that is different from galls caused by other species. The gall provides some protection from adverse weather, predators and parasites.
Galls are rich in proteins and carbohydrates.
Thus the gall-maker lives a sheltered, luxurious life surrounded by a ready source of food in which it grows, develops and even reproduces. The new adult gall-makers emerge from the galls in the summer or the following spring. Despite their unsightly appearance, most insect galls do not seriously affect the vigor of healthy plants. Occasionally, a heavy or prolonged gall infestation on small branches or roots may weaken or kill portions of a tree. That is, spraying or treating does not make them go away.