Wingspan 10-12 mm.
Occurring widely in England and southern Scotland, less so in Wales and Ireland, this species is relatively common in damp habitats such as river and canal banks and marshes.
The small white and blackish adult is quite distinctive, and flies between May and August in one or two broods depending on latitude.
The larvae mine the stems of reed canary-grass (Phalaris arundiacea) and common reed (Phragmites australis); occasionally on other grasses. The pupa is anchored externally on the foodplant by a silken girdle.