Delina nigrita
A smallish, elongate, shining black fly. Frons yellow, face and jowls white. Palpi dark. Propleuron and front coxa white dusted. Halteres yellow. Femora dark except very narrowly at the knees. Tibia yellow, tarsi brownish. Wings unmarked with yellowish brown veins. Wing length: ♂ 3.5 - 3.6 - 3.7 mm (3); ♀ 3.7 - 4.1 - 4.5 mm (6).
The larvae mine the leaves of orchids forming a linear mine which extends from the egg which is deposited on the upper surface of a leaf. Marsh orchids (Dactylorhiza spp.) are the most frequent host plant, but Hackman (1956)[1] records it from Plantanthera and Orchis. I have found it in poor fen and moorland situations in Scotland, including at high altitude on Cairngorm (approx. 915m), where Heath spotted orchid (Dactylorhiza maculata) was abundant. Adults fly in June and July.
References
Widespread but scarce in damp grasslands. Irwin (1975)[1] records it from Ireland and notes a record of a marsh orchid in a Belfast garden infested with large numbers of larvae.
World distribution: Palaearctic: Austria, Czech Republic, Denmark, Estonia, Finland, France, Germany, Ireland, Lithuania, Netherlands, Norway, Poland, Slovakia, Spain, Sweden, Switzerland; Russia: European regions and eastern Palaearctic; Asia, Mongolia; Nearctic: Canada, USA (Alaska).