gallfly

/ˈɡɔlˌflaɪ/
noun
  1. A small insect that lays its eggs in plant tissues, causing the plant to form a growth called a gall.
    • The gallfly laid its eggs on the oak leaf, and a round gall formed around them.
    • Each species of gallfly usually attacks only one specific type of plant.
    • Farmers sometimes worry about gallflies damaging their crops.