Protocalliphora

Protocalliphora or bird blowflies are a blow fly genus containing many species which are obligate parasites of birds. Eggs are laid in bird nests. After hatching, the larvae suck the blood of nestlings. They sometimes feed inside the nostrils of nestling birds and destroy the tissue at the base leading to reduced growth of the upper mandible and the young growing with "shovel-beaks". The species overwinter as adults.