Males are unknown. The female is black except for a small area around the base of the sawsheath, the antennal scape and the tegulae. The stigma is strongly infuscated but pale basally. In dorsal view, setae on the sides of the sawsheath are sparce and concentrated towards the apex.
Heptamelus dahlbomi larvae feed within the petiole of lady fern leaves. More common on cultivated ferns than Heptamelus ochroleucus.
Size: 3.5 - 5.5mm
Distribution: England, Scotland, Ireland
Flight period: May to June
Plant associations: Anthyrium filix-femina (lady fern)
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
Vikberg, Veli & Liston, Andrew. (2009). Taxonomy And Biology Of European Heptamelini (Hymenoptera, Tenthredinidae, Selandriinae). Zootaxa. 2112. 1-24. 10.5281/zenodo.187915.