[AS.] A name applied to many of the winged insects, but scientifically restricted to the sub-order Diptera, which have two wings and whose mouth-parts are converted into a sucker, used for taking up fluids. The sucker acts as a lancet, by which the skin of animals and vegetables is pierced so as to reach the blood or sap. The flies comprise many thousands of species, differing greatly in size, the best known being the common house-fly.