You can see evidence of insects everywhere, especially on plants. Galls on leaves, twigs, buds, stems, and roots are most often the result of insect activity. What, exactly, are galls?
Galls are abnormal growths of plant tissue trigger in response to an injury to or an irritation of the plant, usually (but not always) caused by some living organism. Nematodes, bacteria, fungi, and viruses can all cause the formation of galls on trees, shrubs, and other plants. Most galls, however, result from insect or mite activity.