Nematus alniastri (formerly Craesus alniasti)
One of four Nematus species in Britain and Ireland characterised by the enlarged basitarsal segment. This species is shining in the centre of the upper part of the mesopleura such that the punctures are not obscured (Nematus brischkei has fine microsculpture here). The femora are mainly yellow with any infuscation confined to the base and extreme apex. Males are rare.
Nematus alniastri larvae feed on alders and are parasitised by the wasp Excavarus apiarius.
Size: 7.5 to 8mm
Distribution: England, Scotland, Wales, Ireland
Flight period: Bivoltine. May to June and July 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