Stromboceros delicatulus - Delicate Fern-sawfly

Recorded widely across all of mainland Britain, and in Orkney; can be common amongst ferns (Musgrove, 2023).

The only species of this genus to be represented here. The long, slender insect is predominantly light green to pale yellow with a black head, black patches on the mesonotum and a distinct black patch covering the mesosternum. Colour fades to straw in death. The abdomen may also be marked with black in part.

Stromboceros delicatulus larvae feed on ferns, including bracken, in woodland. Larvae are green with bristled warts and two dark elongate spots on the vertex. When disturbed they fall to the ground, thrashing wildly from side to side in the way that some lepidopteran caterpillars do. Mature larvae go to ground after emptying the gut but before changing into the eonymph.

Jump to information on the genus Stromboceros

Size: 5.5 to 7mm

GB IUCN Status: Least Concern
GB Rarity Status: None

Distribution: England, Scotland, Wales, Ireland

Flight period: May to September

Plant associations: Pteridium spp., Dryopteris spp., Onoclea spp., and Polypodium spp. (ferns and bracken)


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.

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 Natural England, unpublished