The adult has a purple-brown forewing with shining white fascia beyond the middle but identification of adults is very difficult and this species is best recorded from the larval mine.  The larvae mine the leaves of Apple species producing a sinuous gallery, widening later, with linear frass.

Adult Leafmine  

Adult: It may not be possible to identify adults to species level, even by gen det.

Leafmine: There are other mines on apple that are quite similar to Stigmella malella mines and great care is needed. A photograph is required showing the backlit mine and the larva if present. Please state the host species when submitting your record.

Where Apple trees occur.

Mines may be seen June to July and then September to October.

Fairly widespread, but local in England and Wales. In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified as local.

Leaf mining activity has shown this species to be more common than previously thought in Leicestershire and Rutland..

http://www.leafmines.co.uk/html/Lepidoptera/S.malella.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/lepidoptera/monotrysia/nepticuloidea/nepticulidae/stigmella/stigmella-malella/