Recorded widely throughout most of England and Wales, with Scottish records currently restricted to Aberdeen (Musgrove, 2023).
Outbreaks of large populations have become more common in recent years defoliating trees, especially in city locations: Telford, Manchester, Aberdeen. A black, slow moving species with dark wings. Sometimes the front legs are piceous.
Tomostethus nigritus larvae feed gregariously on the native common ash and on the continent have been seen to use municipally planted narrow-leaved ash.
Size: 7 - 8mm
GB IUCN Status: Least Concern
GB Rarity Status: None
Distribution: England, Scotland, Wales, Ireland
Flight period: April to June
Plant associations: Fraxinus spp. including Fraxinus excelsior and Fraxinus angustifolia (ashes including common ash and narrow-leaved 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
Musgrove, A.J. 2023. A review of the status of sawflies of Great Britain - Phase 2: The Athaliidae and the Tenthredinidae (excluding Nematinae). Natural England, unpublished
Verheyde, F. and Sioen, G., 2019. Outbreaks of Tomostethus nigritus (Fabricius, 1804)(Hymenoptera, Tenthredinidae) on Fraxinus angustifolia ‘Raywood’in Belgium. Journal of Hymenoptera Research, 72, p.67.
Taylor, F.S., 2014. An outbreak of Tomostethus nigritus (F.) (Hymenoptera: Tenthredinidae) on Aberdeen’s urban ash trees. British Journal of Entomology and Natural History, vol. 27 pp 190-191.