The maggots of some species, raised under sterile conditions, are currently being used by some doctors as microsurgeons to clean necrotic tissue from difficult wounds, with excellent results. The maggots of some flies are predatory. Some fly species have been used for biological control because their larvae are parasitic on the larvae of some plant pests. The maggots of some flower flies can be found feeding on aphids. Flies have one pair of normal wings.
Halteres are sense organs which are essential for stable flight.
In flight, the halteres move up while the wings are moving down and down while the wings are moving up. In many species they also oscillate during walking. The halteres of the crane fly can be easily seen. The adults of some species do not eat. While you are out exploring, watch for flies.