Little wooden spheres attached to dry stalks in meadows are homes to the larvae of a certain fly. You can see them in patches of meadow where ever goldenrod grows. As the plant grows, a fly lays an egg into the growing tip.  The hatchling larva releases chemicals that compel the plant to produce a golf-ball size growth called a "gall".  If you lived in a house lined entirely with edible plant material, you'd have an approximation of a gall.  This episode describes the biology of goldenrod galls and suggests ways to use them for educational purposes.