Many insects are valuable as predators on the harmful species, and some are important as scavengers and as aerators of the soil (see scarab beetle). Most important, many plants depend on insects as agents of pollination; in fact, flowering plants and insects evolved together. Insects are the source of useful products such as honey, beeswax, silk, lac, and cochineal. They are a major source of food for many animals, and some are eaten by humans in many parts of the world. The fruit fly has been the major experimental animal used in genetics.