From Wikipedia:
Anthomyzidae are small, slender, yellow to black flies with narrow and elongate wings, which may have distinct markings. Some species have greatly reduced wings. Fewer than 50 species are known, mostly from Europe. Although they occur in all major regions, they seem to be most varied in the Holarctic Region.
Biology: Larvae have been reported from decaying dicotyledonous plants, and from fungi and , in Europe, from leaf sheaths of various grasses and of Typha and Juncus, from Lipara galls on Phragmites, It is possible that they may be either phytophagous or saprophagous, but there seem to be no reports of damage to cereals or other plants.

---