Wingspan 9 to 12 mm. The adult moth is dark blackish in colour and often has a violet reflection. It lacks the white tornal spot of P. filicivora.  The larva mine the leaves of various ferns including Hart's-tongue Fern and Polypody, feeding on the underside and occasonally making a blotch mine in the leaf.  An untidy mass of fern sporangia usually indicates the presence of the larva, which has a black head, pronotum and anal plate

Psychoides filicivora, with paler head, etc, 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.

In areas with suitable amounts of the larval foodplants.

Adult: May to July.

Larva (early and late instars) has black head, prothoracic shield and anal plate, which distinguish it from the other fern frond species, P. filicivora. It mines mature fern frond with well developed sporangia, usually Hart's-tongue, and makes case (vacant when larva in frond) resembling displaced sorus (spore body). Aug.-June, most prominent April-May. Pupal case has sharp crest when unworn.

Local in distribution and mainly found in the southern half of Britain. In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified as local.

It appears to be uncommon 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.verhuella.htm

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