Wingspan 9 to 14 mm. A small purple and gold moth, there are similar species and detailed examination is required for a safe id.

All Eriocraniidae leafmines have spaghetti-like frass, in long threads.  The larva of Eriocrania sangii is unusual in being grey.  This colour can sometimes be seen in a backlit mine, or retained in cast larval skin.

Other Eriocrania on Birch

Adult leafmine+larva

When recording the mine, ensure that the larva or cast larval skin is photographed as well as the backlit mine

Well wooded areas containing Birch.

The adults fly in March and April.

The larva creates a blotch mine in a leaf of birch (Betula), rather like some related species, but unlike the other species, the larva itself is dark grey and is quite distinctive if the mined leaf is held up to the light.

Locally frequent, especially in northern England. 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/E.sangii.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/lepidoptera/glossata/eriocraniidae/eriocrania/eriocrania-sangii/