''Carnus hemapterus'' is a Dipteran

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs ...

, a small-bodied and partly black-coloured carnid fly. In their adult stage of life, they are blood-sucking

ectoparasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...

s of nestling birds. Within the genus ''Carnus'', this is the only species widespread across Europe and the cold and temperate regions of Asia and North America. Female body length is about 1.5 mm, males are smaller. It typically occurs in the nests of medium- to large-bodied birds, provided that the nest is not on the ground. It is particularly common on the chicks of

owls Owls are birds from the order Strigiformes (), which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers ...

falcon Falcons () are birds of prey in the genus ''Falco'', which includes about 40 species. Falcons are widely distributed on all continents of the world except Antarctica, though closely related raptors did occur there in the Eocene. Adult falcons ...

s, rollers,

bee-eaters The bee-eaters are a group of non-passerine birds in the family Meropidae, containing three genera and thirty species. Most species are found in Africa and Asia, with a few in southern Europe, Australia, and New Guinea. They are characterised b ...

and

starlings Starlings are small to medium-sized passerine birds in the family Sturnidae. The Sturnidae are named for the genus '' Sturnus'', which in turn comes from the Latin word for starling, ''sturnus''. Many Asian species, particularly the larger ones, ...

. Females give birth to larvae that live within the nest and feed on organic debris and the pupae also overwinter there. The emergence of imagines is synchronized to the hatch of host nestlings in the subsequent year. They prefer larger chicks within the nest. Adult flies have a winged and an unwinged variety, the latter being more common. In fact, unwinged flies still carry the basal part of their wings, but the majority of the wing is broken off (see a close view of the above photo). Flies live only on the nestlings before and during the development of the plumage, and disappear later on. Infestations by ''Carnus hemapterus'' appear to be rather harmless for the host chicks. In spite of that,

barn owl The barn owl (''Tyto alba'') is the most widely distributed species of owl in the world and one of the most widespread of all species of birds, being found almost everywhere except for the polar and desert regions, Asia north of the Himala ...

females advertise their resistance genes by the dark spots on their breast and belly; nestlings of heavily spotted females tend to be more resistant. In this study, potential environmental confounding effects were controlled for by cross-fostering chicks. The faeces and blood remains from these ectoparasitic flies make spots on the eggshell surface of host birds. This contamination appear to increase abundance and diversity of eggshell bacterial loads and, consequently, increase the chance of embryo death. Image:Barnowl.jpg, Barn owl, heavily spotted Image:Schleiereule-IMG 4064.JPG, Barn owl, medium coloration Image:Tyto alba close up.jpg, Barn owl, weakly spotted

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Further reading