The Fly

A fly (pl. flies) is an insect of the order Diptera (from Ancient Greek δι- di- 'two' and πτερόν pteron 'wing'), named for the single pair of wings. The hindwings have evolved into halteres, organs that sense rotation, giving flies precise control of their flight. Diptera is a large order containing more than 150,000 species, including horse-flies, crane flies, hoverflies, mosquitoes and others. Flies have a mobile head, with a pair of large compound eyes, and mouthparts designed either for piercing and sucking (in mosquitoes, black flies, and robber flies) or for lapping and sucking (in the other groups). Their wing arrangement gives them great manoeuvrability in flight, and claws and pads on their feet enable them to cling to smooth surfaces. Flies undergo complete metamorphosis; the eggs are often laid on the larval food-source and the larvae, which lack true limbs, develop in a protected environment, often inside their food source. Other species are ovoviviparous, opportunistically depositing hatched or hatching larvae, instead of eggs, on carrion, dung, decaying material, or open wounds of mammals. The pupa is a tough capsule from which the adult emerges when ready to do so; flies mostly have short lives as adults. Diptera is one of the major insect orders and of considerable ecological and human importance. Flies are major pollinators, second only to bees and their Hymenopteran relatives. Flies may have been among the evolutionarily earliest pollinators responsible for early plant pollination. Fruit flies are used as model organisms in research, but less benignly, mosquitoes are vectors for malaria, dengue, West Nile fever, yellow fever, encephalitis, and other infectious diseases; and houseflies, commensal with humans all over the world, spread foodborne illnesses. Flies can be annoyances, especially in some parts of the world where they can occur in large numbers, buzzing and settling on the skin or eyes to bite or seek fluids. Larger flies, such as tsetse flies and screwworms, cause significant economic harm to cattle. Blowfly larvae, known as gentles, and other dipteran larvae, known more generally as maggots, are used as fishing bait, as food for carnivorous animals, and in medicine in debridement, to clean wounds.