Encyclopedia fly fly, name commonly used for any of a variety of winged insects , but properly restricted to members of the order Diptera, the true flies, which includes the housefly , gnat , midge , mosquito , and tsetse fly . The hind wings are reduced to knobbed balancing organs called halteres. All flies undergo complete metamorphosis , i.e., a four-stage development.
Many flies are harmful either as carriers of disease or as destroyers of crops.
Some parasitize harmful insects. Some, such as the fruit fly, are important in laboratory studies. Flies are classified in the phylum Arthropoda , class Insecta, order Diptera. Licensed from Columbia University Press.