fly

Any insect of the order Diptera. A fly has a single pair of wings, antennae, and compound eyes; the hind wings have become modified into knoblike projections (halteres) used to maintain equilibrium in flight. There are over 90,000 species.

The mouthparts project from the head as a proboscis used for sucking fluids, modified in some species, such as mosquitoes, to pierce a victim's skin and suck blood. Discs at the ends of hairs on their feet secrete a fluid enabling them to walk up walls and across ceilings. Flies undergo complete metamorphosis; their larvae (maggots) are without true legs, and the pupae are rarely enclosed in a cocoon. The sexes are similar and coloration is rarely vivid, though some are metallic green or blue. The fruitfly, genus Drosophila, is much used in genetic experiments as it is easy to keep, fast-breeding, and has easily visible chromosomes.