Cheilosia caerulescens
Species belonging to the genus Cheilosia are black mainly. There are some 40 species (at least here in the Benelux), all very similar. Many species will reach a length of well over 10 mm. Sofar we have identified only one: Cheilosia caerulescens, of which you can see the pictures here. For identification look for these characteristics: the eyes are hairless, the legs are partially brownish yellow, the scutellum is black and the middle vein in the wing is darkened. Chances are however you'll never see it, for as far as we know it is not a British species.
