Behaviour
Common Barn owl nestlings hosts to Carnus hemapterus. © Wikipedia
Carnus hemapterus is an ectoparasite which sucks blood of nestling birds (Walter & Hudde 1987 , Kirkpatrick & Colvin 1989, Dawson & Bortolotti 1997, Roulin 1998). After locating the host, adult flies loose their wings and start sucking the blood of the nestlings. The females lay their eggs in the nest, where the larvae then develop feeding on organic nest material.
Carnus hemapterus is found on cavity nesting birds or in nest above the ground (Bequaert 1942) and has been recorded from over 40 bird species in 18 families (Grimaldi 1997).
Because neither the adults nor the larvae have been found on adult birds, flies are assumed to colonize nest hosts actively during the winged phase of their life cycle (Grimaldi 1997, Roulin 1998, 1999).
The occurence of the flies is correlated with the breeding season of the birds. For example in Spain adult Carnus hemapterus flies emerged from the fourth week of May until the first week of July with a peak in the second week of June (Valera et al. 2003)