Unknown larva on alder

Unknown larva on alder

Observation - Unknown larva on alder - UK and Ireland. Description: Have seen these before but not sure I've ever worked out what they are. On alder leaf at edge of Whitlingham Great Broad. Advice welcome! (Note - next to leaf mine of Phyllonorycter froelichiella, but not that.

Have seen these before but not sure I've ever worked out what they are. On alder leaf at edge of Whitlingham Great Broad. Advice welcome! (Note - next to leaf mine of Phyllonorycter froelichiella, but not that.