Heterarthrus vagans


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.

Identification difficulty

Adult, Larva and leafmine (when the host plant is identified)


Where Alder is present.

When to see it

Larval mines may be seen whilst Alder is in leaf especially towards autumn.

Life History

The species is univoltine with larva being present towards autumn.

UK Status

Widespread, but less common than Fenusa dohrnii which also mines Alder species.

VC55 Status

Status in Leicestershire and Rutland not known.

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Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map