Abdomen mostly black above and with dark stigma. The underside of the abdomen is extensively white. The tergites either have black apical margins, or else have narrow white margins that do not broaden on the mid-dorsal line. The species has a diagonal median black stripe in addition to the black margins and a black sterno-pleural longitudinal band. The similar Pachyprotasis similans and variegata lack the diagonal stripe.
Pachyprotasis rapae larvae feed on a broad range of plants.
Size: 7 - 8mm
Distribution: England, Scotland, Wales, Ireland
Flight period: May to July
Plant associations: Betonica spp., Scrophularia spp., Solidago spp. and Fraxinus spp. (betony, figwort, golden rod and ash)
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