The insects bearing this name belong to the order of the Diptera, which includes more than 4 thousand different species, and are widespread throughout the world. Their dimensions can vary from a dozen millimeters to a centimeter or a little more. All are characterized by a juvenile phase, in which they have the appearance of a whitish conical-shaped larva, during which they feed on plants, living flesh, parts of dead animals, or are parasites of superior animals. An example: there are fly larvae that live in the lower part of the intestine of mammals, including humans, and which particularly affect children who swallow their eggs by playing with the earth. As adults, and therefore when they have undergone the transformation that leads them to have wings, these insects prefer instead to suck the sugary liquids of the plants, or the blood. Their life is about three weeks.