Heptamelus dahlbomi - Dahlbom's Shorthorn
Originally described by Thomson in 1870, this species was not recognised by Benson (1951). It was re-described by Vikberg & Liston (2009)and to date, all records that have come to light are from the western side of Britain between 1936 and 2001, including from Cornwall, through the West Midlands to Cumbria and on Argyll and the Isle of Barra. It seems highly likely that further examination of old specimens originally attributed to ochroleucus will reveal more dahlbomi. The fact that five records were generated from collected larvae in a ten-day period in Cumbria suggests that this species is very overlooked (Musgrove, 2022).
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
GB IUCN Status: Data Deficiency
GB Rarity Status: Nationally Rare
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
Musgrove, A.J. 2022. A review of the status of sawflies of Great Britain - Phase 1: families other than Tenthredinidae. Natural England, unpublished
Vikberg, Veli & Liston, Andrew. (2009). Taxonomy And Biology Of European Heptamelini (Hymenoptera, Tenthredinidae, Selandriinae). Zootaxa. 2112. 1-24. 10.5281/zenodo.187915.