In the female, the head and mesonotum and the underside of the antennae are orange-red whilst the underside of the thorax and the abdomen are entirely black. The costa is yellow with the stigma and remaining venation dark. In the male, the antennae are similarly red below and with a dark stigma.
Hemichroa australis larvae usually feed singly on the leaves of alder or birch. Initially they feed on the leaf creating a J-shaped hole in the leaf blade. Later instars feed at the edge of the leaf, eating the entire leaf. The tail is held curled downwards. Mature larvae have yellow heads with a black eye spot. The thoracic segments have yellowish spiracular and suprapedal lobes. The tail of the larva is marked with yellow dorsally.
Size: Female: 5 - 8mm, male 5 - 6mm
Distribution: England, Scotland, Wales, Ireland
Flight period: Bivoltine, May to June and July to August
Plant associations: Alnus spp. and Betula spp. (alders and birches)
Benson, R.B., 1952. Handbooks for the Identification of British Insects. Hymenoptera, Symphyta, Vol 6, Section 2(a-c), Royal Entomological Society, London
Chevin, H. 1998: Biologie d'Hemichroa australis (Lepeletier, 1823) (= H. alni L., 1767) (Hym. Tenthredinidae, Nematinae). - Bulletin des Naturalistes des Yvelines, Versailles ser. 5, 25: 7-11
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