Carnus hemapterus is a Dipteran insect, a small-bodied and partly black-coloured carnid fly.

Within the genus Carnus, this is the only species widespread across Europe and the cold and temperate regions of Asia and North America.

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.

The faeces and blood remains from these ectoparasitic flies make spots on the eggshell surface of host birds.