Wingspan 24-40 mm.
A sexually dimorphic species, with the females paler in colour and generally larger than the males. Both sexes have distinctively long labial palps.
It occupies fens and other wet places where large reedbeds occur, and is found mainly in England and Wales where it flies in June and July.
The whitish caterpillars feed inside the stems of common reed (Phragmites australis) and reed sweet-grass (Glyceria maxima).