The Fen Wainscot (Arenostola phragmitidis) is a moth of the Noctuidae family. It is found in most of Europe (except Ireland, Iceland, the Iberian Peninsula and the western part of the Balkan Peninsula), western Siberia, Turkey, Iraq, Afghanistan, central Asia and China. The wingspan is 32–36 mm. Adults are on wing from July to August. The larvae feed internally in the stems of Phragmites australis.