Tenthredopsis nassata (Linnaeus, 1767)

Tenthredopsis nassata

Recorded from the whole of mainland Britain as well as Orkney; one of the most frequently recorded sawfly species. Benson (1952) included scutellaris within nassata, and so records will be conflated to some extent. However, more recent records are mostly nassata and assessment of the dataset should give a broadly accurata picture (Musgrove, 2023).

As with all Tenthredopsis species Tenthredopsis nassata is variable in colour. The description given here follows Blank and Ritzau 1998 but it should be noted that British specimens may differ in colour from continental counterparts.

In typical females the ground colour is orange-brown. The abdomen often has a dorsal, black longitudinal stripe, but there is no stripe on the ventral surface. The hypopygium centrally is triangular and only slightly indented at the apex.
A black and red form of the female is sometimes encountered.

The male cannot easily be distinguished from Tenthredopsis scutellaris but scutellaris is smaller than nassata. The mesepisternum is often darkened with the pectus usually completely black. The hind tarsi are more or less uniformly light or dark. There is a midline keel on the eighth tergite, which often reaches the base of the tergite. On either side of the keel there is a deep and somewhat oval-shaped depression, at least from the posterior margin to the middle and often to the base of the tergite.

Larvae feed on grasses especially cock's-foot, tufted-hair grass and wavy-hair grass.

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Size: Female: 10 - 12mm, male: 8 - 11mm.

GB IUCN Status: Least Concern
GB Rarity Status: None

Distribution: England, Scotland, Wales, Ireland

Flight period: May to August

Plant associations: Gramineae especially Dactylis glomerata, Deschampsia caespitosa and Deschampsia flexuosa (grasses especially cock's-foot, tufted-hair grass and wavy-hair grass).