The larvae of the sawfly Heterarthrus vagans mine the leaves of Alder species. The white larva has a distinctive black mark near the head followed by 3 spots. It creates a large blotch that normally starts at, or near, the leaf margin, where some or much frass is ejected. The mine is brownish and the full grown larva makes a disc-shaped cocoon.
Where Alder is present.
Larval mines may be seen whilst Alder is in leaf especially towards autumn.
The species is univoltine with larva being present towards autumn.
Widespread, but less common than Fenusa dohrnii which also mines Alder species.
Status in Leicestershire and Rutland not known.
Leicestershire & Rutland Map
Enter a town or village to see local records