Males are not known. Antennae are longer than the thorax with the third segment at most 1.5 times as long as broad, but with the fourth and fifth segments each more than twice as long as broad.
Fenusa dohrnii larvae mine the leaves of alder trees and can be confused with Heterarthrus vagans mines. However, Fenusa dohrnii mines are often present in multiples in one leaf whereas vagans tend to occur singly. This alone is not sufficient to identify accurately.
Size: 3 - 4mm
Distribution: England, Scotland, Wales, Ireland
Flight period: Bivoltine, May to June and August.
Plant associations: Alnus spp. (alder)
Benson, R.B., 1952. Handbooks for the Identification of British Insects. Hymenoptera, Symphyta, Vol 6, Section 2(a-c), Royal Entomological Society, London
Liston A, Knight G, Sheppard D, Broad G, Livermore L (2014) Checklist of British and Irish Hymenoptera - Sawflies, ‘Symphyta’. Biodiversity Data Journal 2: e1168. https://doi.org/10.3897/BDJ.2.e1168