Milichiidae are a family of flies. Most species are very small and dark. Details of their biology have not yet been properly studied, but they are best known as kleptoparasites of predatory invertebrates, and accordingly are commonly known as freeloader flies or jackal flies. However, because of the conditions under which many species breed out, they also are known as filth flies.
The Milichiidae are a family of flies in the suborder Brachycera. They were at one time included in the family Carnidae. At one time or another they have been assigned to various superfamilies, including Carnoidea, Chloropoidea, and Agromyzoidea. As usual for flies of these groups, Milichiidae imagines are tiny, but their heads are comparatively large, compared to many fly species of the same size, such as those in the family Phoridae.
Milichiidae are small-to-very-small flies, usually 1 to 3 mm in length. Typically they are black or at least dark. In some species, such as Milichiella argyrogaster, the abdomen of the male is silvery on its dorsal surface because of a covering of fine hairs. The eyes of Milichiidae are often red, though this need not be obvious because many species of the flies are small and dusky. Though the proboscis is fairly long in most species, this is not obvious because it commonly is geniculate, having a knee-like fold in the middle that holds it inconspicuously beneath the head when the animal is not feeding. When it is looking for a place to feed on the prey of a spider or the like, the proboscis is extended, giving an impression of licking, as shown in the accompanying video. The abdomen is short and broad; it may be impressively distended after a large meal, as shown in the accompanying photographs.
