According to Prous et al, 2019, there is currently no reliable key or species treatment available for this genus. The description follows Benson (Priophorus laevifrons).
The head on the frons and temples above smooth and shining without sculpture or hair-warts. Cladius ulmi is a black sawfly with pale tibiae and tarsi on all legs. The wings are subhyaline. The abdomen without any brown spot in the middle of the first tergite.
Larvae feed on elm creating holes in the leaf surface between the veins. They can be distinguished from the other elm feeding species, Cladius rufipes, by the presence of a black spot on the front of the face which is absent in rufipes.
Size: 5 - 6.5mm
Distribution: England, Scotland, Wales, Ireland
Flight period: Bivoltine, May to August
Plant associations: Ulmus spp. (elms)
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. 2003: Biologie et description de la larve de Priophorus ulmi (Linné, 1758) (Hymenoptera, Tenthredinidae, Cladiinae). - Bulletin des Naturalistes des Yvelines, Versailles 30: 61-64.
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
Prous, M., Liston, A., Kramp, K., Savina, H., Vårdal, H. and Taeger, A., 2019. The West Palaearctic genera of Nematinae (Hymenoptera, Tenthredinidae). ZooKeys, 875, p.63.