Wingspan 4 to 4.6 mm. The adult moths are similar to several other species in the group, and it may not be possible to identify adult to species level even by gen det. The larvae mine various Birch species.  The gallery is almost filled with coiled frass, leaving an intermittent transparent zone at either side. The corridor mostly begins close to the leaf margin, often near the tip of the leaf. The egg is usually on the underside of leaf.  

Stigmella continuella also has coiled frass

Adult Leafmine  

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

Leafmine: A photograph of the mine which must be backlit to show the frass pattern.  Note the host plant and if possible the egg position.

Where Birch, the larval host species, is present.

Adults are on wing in May and again from July to August.

Pupation takes place outside of the mine.

In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified as local.

Rare, or rarely recorded, in Leicestershire and Rutland. The Leicester, Gilroes Cemetery record of 8th November 2019 was the first for Leicestershire and Rutland.

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

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