The head and abdomen colour in this species is highly variable. The thorax is usually black with a pale edge to the pronotum. The hind femora are usually pale but occasionally dark in the basal one-half. In the female the abdomen is usually reddish-yellow above with basal and apical tergites darkened but may be completely darkened. In the male, the abdomen is usually darkened above and often below.
Heretarthrus vagans larvae mine the leaves of alders and form a blister mine. Within the mine they form a circular cocoon which remains in the leaf.
Size: Female: 3 - 6mm, male: 2.5 - 4.5mm
Distribution: England, Scotland, Wales, Ireland
Flight period: Bivoltine, May to September
Plant associations: Alnus spp. (alders)
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
The National Biodiversity Network records are shown on the map below. (See terms and conditions)
Liston, A., Mutanen, M. and Viitasaari, M., 2019. On the taxonomy of Heterarthrus (Hymenoptera, Tenthredinidae), with a review of the West Palaearctic species. Journal of Hymenoptera Research, 72, p.83.