The larvae of the fly Agromyza alnivora mine the leaves of various species of Alder creating an upper surface gallery, narrow at first but, widening considerably towards the end.
Leafmine occurs on Alder. http://www.leafmines.co.uk/html/Diptera/A.alnivora.htm
Where Alder, the larval foodplant is present.
Mines may be encountered when Alder is in leaf especially in summer and early autumn.
Widespread but rather local in Britain.
Status in Leicestershire and Rutland not known.
Leicestershire & Rutland Map
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Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015