Thick-headed Flies in Nottinghamshire
Thick-headed Flies belong to the Conopidae family, but certain anatomical features, suggest that they are closely related to hoverflies. Several species are excellent wasp mimics and the larvae of this parasitic family feed internally in bees and wasps. The adults are nectar feeders, regularly visiting flowers.

One Thick-headed Fly (Conops quadrifasciata) specialises in feeding on bumblebees - waiting near flowers for a bee to arrive, piercing the body and quickly depositing an egg inside. The egg hatches and the larva feed off the abdominal contents of the bumblebee for about 10 days, effectively hollowing it out and filling almost the entire abdominal cavity. The larva pupates inside the bee becoming an adult fly the next summer. Parasitised bees appear to change the behaviour and tend to stay outside the nest more than other workers, often remaining outside even in very cold weather.

Conops vesicularis (Linnaeus, 1761)
Photographed in Sherwood Forest on 30/05/06
Conops quadrifasciatus (De Geer, 1776)
Photographed at Warsop Wood, Nottinghamshire on 26/07/06
Conops flavipes (Linnaeus, 1758)
Photographed at Clipstone Old Quarter, Sherwood Forest Nottinghamshire on 14/08/06
Physocephala rufipes (Fabricius, 1781)
Photographed near Walesby, Nottinghamshire on 25/07/06
Sicus ferrugineus (Linnaeus, 1761)
Photographed near Carburton, Nottinghamshire on 29/07/06
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