Wingspan 10 to 12 mm. The light patches on the dark wings of his moth form an approximate diamond shape when the wings are together.  The larva mine the leaves of various ferns including Hart's-tongue Fern, Dryopteris spp. and Polypody, feeding on the underside of the frond and occasionally making a blotch mine in the leaf.  An untidy mass of fern sporangia usually indicates the presence of the larva, which has a brown head and pronotum.

Psychoides verhuella is similar but lacks the light diamond patch on the wings. The larva are similar; an image showing both larval species for comparison is available here.

Adult leaf mine

Only mature tenanted mines can be recorded.  Provide backlit photograph oof the underside of the fern frond; note host species. Provide photo of late instar larva showing head/pronotum colouration.

The species occurs in areas that are rich in ferns, but is also sometimes found indoors.

The moths fly during the daytime in an extended generation throughout the summer, but because it can be found on indoor fern plants, it may also be encountered occasionally during the winter months as well.

The larvae feed on various ferns. It is possible that the species has been introduced from abroad with imported ferns.

Discovered in Ireland in 1909, this species has since been found in a number of English and Welsh counties, mainly coastally. In the Butterfly Conservation’s Microlepidoptera Report 2011 this species was classified as local.

Rare in Leicestershire and Rutland, where there are few records. L&R Moth Group status = D (rare or rarely recorded).

http://www.leafmines.co.uk/html/Lepidoptera/P.filicivora.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/lepidoptera/ditrysia/tineoidea/tineidae/teichobiinae/psychoides/psychoides-filicivora/