page_title: Milichiidae
section_title: Biology
hierarchical_section_title: Milichiidae / Biology
caption_attribution_description: English: Desmometopa spec. det. Irina Brake (2007), Milichiidae, in front of Rhinocoris erythropus, Kaub, Germany
context_page_description: 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.
context_section_description: The larval stage generally lasts about 2–3 weeks in temperate climates. Larvae primarily feed on rotting vegetable matter or decaying wood or bark and may be reared from manure or decaying plant materials. At least some are coprophagous and feed on human ordure and other detritus, hence the common name "filth flies". At least some species may breed in dead fish and other carrion, a point of possible interest in forensic entomology.
  Some species also have been recovered or reared from birds' nests and bat roosts, but reports of parasitism on birds' nestlings by Milichiidae should be interpreted with caution; at one time Milichiidae and Carnidae were not regarded as separate families, and it is not always clear how many of such reports refer to any species other than those that nowadays are included in the Carnidae and separated from the Milichiidae.
  Human commerce has inadvertently spread some species to all continents but Antarctica. Examples include members of the genera Desmometopa and Milichiella.
  The adults of some species linger close to invertebrate predators, where they act as kleptoparasites, feeding on bodily fluids of the prey. This strategy has given rise to a range of common names such as freeloader flies and  jackal flies. The nature of the kleptoparasitism that Milichiidae practise is difficult to detect from direct observation; some observers remark that they seem to lick the prey rather than anything else. However, it seems that they get whatever nourishment they can; the accompanying photographs suggest that at least some species penetrate the thinnest cuticle of a bee in a spider's jaws, extracting tissues that enzymes in the venom of the spider have reduced to a fluid state. When extended, the proboscis certainly is long enough for feeding in such a manner.
  The "jackal" habit has been widely documented, with many pictures and references to Millichiidae assembling on the prey of spiders (especially Nephilinae, Oxyopidae, and Thomisidae). They also visit Asilidae, Reduviidae, and even Mantodea. However, a point that is rarely mentioned is that most prey insects do not attract Milichiidae particularly. Instead they seem only to follow the scents exuded by killed prey such as Hemiptera, Heteroptera (stink bugs), and Hymenoptera. This is compatible with the fact that photographs of Milichiidae on prey, almost universally show them on insects that provide such olfactory clues. This would be compatible with the idea that predators that commonly hunt prey that release a dramatic and characteristic olfactory signal, thereby create a niche for suitable kleptoparasites. In at least species that are attracted to prey of Nephilinae in Florida, the major attractants released by Heteropteran prey appear to be low-molecular-weight carbonyl compounds, among which trans-2-hexenal and hexanal are prominent. These compounds are not conspicuous among those released by captured honeybees, so other classes of attractants are likely to be significant as well. In general there is suggestive evidence that the kleptoparasitism relies on olfactory clues; for example, some species seem to operate in the dark, and photographs of approaching flies seem to show them flying upwind, which is consistent with scent following.
  A notable point is that spiders' meals can have various forms of significance in nature. For one thing, though they may be the most conspicuous of such partakers, the jackal habit is not unique to the Milichiidae, nor do all species in the family necessarily indulge in it, nor for all the same reasons. Certainly careful inspection of photographs of spiders' prey often will show a few specimens from other families of small flies present among the Milichiidae. Examples include Phoridae and Chloropidae. The high frequency of Milichiidae around prey of particular species however, suggests that they are more highly adapted to such activities than most. However, this impression might be regional; reports on field work suggest that in parts of Florida for example, the predominant kleptoparasites were in the family Cecidomy
caption: Milichiidae attending Rhinocoris bugs mating as the female feeds
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