Heterarthrus fiora (naming follows Liston et al, 2019)
Previously misidentified as Heterarthrus aceris (Kaltenbach, 1856). The distribution of this species is somewhat unclear following the recognition that Heterarthrus cuneifrons and wuestneii also occur in Britain. It seems that fiora is the most widespread species however, with recent records throughout much of Britain north into Scotland (Musgrove, 2023). The distribution map of Heterarthrus aceris is given here but is likely to contain records of the three Acer feeding species; fiora, wuestneii and cuneifrons.
This species is entirely parthenogenic. References to males in Benson are believed to be males of either Heterarthrus wuestneii or Heterarthrus cuneifrons. According to Liston, Heterarthrus aceris is a misidentification of this species.
The female is coloured glossy black and off-white. The head is black with a pale labrum, pale margins to the clypeus and a pale inner orbit to the lower half of the eye. The antennae are black with the apical segments reddish-brown. The thorax is black with a pale, narrow margin to the pronotum and pale margins of the tegulae. The abdomen is black with very narrow white margins to the apices of the tergites. The legs are black but pale on the apices of the coxae, femora and more or less the the front surfaces of the tibiae.
Heterarthrus fiora larvae mine the leaves of sycamore starting at the edge of the leaf. A circular cocoon is made from the upper leaf epidermis. This cocoon separates from the leaf prior to the autumn leaf drop leaving a neat hole visible in the leaf. The cocoon works its way into the litter layer.
Size: 3.5 - 4.5mm
GB IUCN Status: Least Concern
GB Rarity Status: None
Distribution: England, Scotland, Wales, Ireland
Flight period: Univoltine, May to June
Plant associations: Acer pseudoplatanus (sycamore)
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
Liston, A., Mutanen, M. and Viitasaari, M., 2019. On the taxonomy of Heterarthrus (Hymenoptera, Tenthredinidae), with a review of the West Palaearctic species. Journal of Hymenoptera Research, 72, p.83.
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