Blasticotoma filiceti - Foaming Fern-borer

Adults are rarely encountered. Recorded from 15 locations to date from Sussex to Cumbria, and with more than half being from Wales. Not located in Scotland as yet (Musgrove, 2022). A slender and mainly black insect with yellowish legs and infuscated wings. Antennae are similar to the Argidae but with a tiny additional segment at the tip. In the forewing the stigma is semicircular and cell 1M is domed outwards apically. 

Larvae of Blasticotoma filiceti feed inside stems of fern fronds and their presence is indicated by a conspicuous walnut-sized froth ball on the frond stem. The froth is attractive to ants and can be found in late July and August by searching ferns.

Jump to Blasticotomidae

Size: Approx. 8mm

GB IUCN Status: Least Concern
GB Rarity Status: Nationally Scarce

Distribution: England, Wales, Ireland

Flight period: May to July

Plant associations: Ferns including Athyrium filix-femina (Lady Fern), Dryopteris spp. (buckler and male ferns), Matteuccia struthiopteris (Ostrich Fern), Polystichum spp. (shield-ferns), Pteridium aquilinum (Bracken)


Benson, R.B., 1952. Handbooks for the Identification of British Insects. Hymenoptera, Symphyta, Vol 6, Section 2(a-c), Royal Entomological Society, London

Benson, R. B. 1953: Re-discovery of the sawfly Blasticotoma filiceti Klug (Hym., Blasticotomidae) in England. - The Entomologist's Monthly Magazine, Fourth Series, London 89(14): 304

Bowdrey, J. P. 2008: Blasticotoma filiceti Klug, 1834 (Sym: Blasticotomidae): a sawfly new to Ireland. - Entomologist's Record and Journal of Variation 120: 123-124.

Forsius, I. 1924: Larven till Blasticotoma filiceti funnen vid Kuopio (Sb.). - Notulae Entomologicae, Helsingfors 4: 95-96

Key, R. S. 1998: The sawfly Blasticotoma filiceti Klug, 1834 (Hym: Blasticotomidae) new to Wales - only the fifth British record. - The Entomologist's Record and Journal of Variation, London 110(1): 34-35

Liston, A., 1995. Compendium of European Sawflies, Chalastos Forestry, Daibersdorf

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. 2022. A review of the status of sawflies of Great Britain - Phase 1: families other than Tenthredinidae. Natural England, unpublished

Shcherbakov, D. E. 2006: Fern sawfly larvae Blasticotoma filiceti Klug, 1834 (Hymenoptera: Blasticotomidae) are visited by ants: a new kind of trophobiosis - Russian Entomological Journal, Moscow 15 (1): 67-72