Wingspan 10-12 mm.
Discovered in Ireland in 1909, this species has since been found in a number of English and Welsh counties, mainly coastally.
The larvae feed on ferns, especially soft shield-fern (Polystichum setiferum) and male-fern (Dropteris filix-mas), but are also found on Hartstongue (Phyllitis scolopendrium). The species is often found indoors.
The moths fly during the daytime in an extended generation throughout the summer. It is possible that the species has been introduced from abroad with imported ferns.
Larva: (Ian F. Smith)
Larvae can be distinguished from the other fern frond species, P. verhuella, by the dark brown to bright green sinuous gut, pale brown head, translucent prothoracic shield with brown posterior margin and the concolorous anal plate. In profile, the head and prothorax are lower than the adjacent part of the body. The larva lives under an irregular mass of sporangia, which is not arranged, as by P. verhuella, into the shape of a sorus.
The pupal case is more rounded than that of P.verhuella, and lacks its keel, but beware of worn specimens of verhuella.