Norellisoma spinimanum
A medium sized, yellowish-brown species with conspicuously spined front legs which give it a raptorial, mantis-like appearance. Readily distinguished from the other two Norellisoma species by its larger size, generally paler appearance and plumose arista. Wing length: ♂ 6.0 - 6.3 - 6.7 mm (4); ♀ 5.3 - 5.8 - 6.3 mm (5).
Larvae mine the stems of docks (Rumex) where they are relatively easy to detect as the stem is typically swollen and reddish around the exit hole. Mines are usually on the main stem, but sometimes also in the leaf petioles (Disney, 1976[1]). He reared the fly from mines in broad-leaved dock, R. obtusifolius and mentions literature records from R. aquaticus in France and the introduced R. triangulivalvis in Britain.
References
Norellisoma spinimanum and Norellia spinipes are frequently confused. They are of similar size and general colouring and the most obvious feature of both are the strongly spined, mantis-like front legs. The feature used in the key: a single row of strong spines on the tibia of Norellia, two rows in Norellisoma; is not actually easy to see, especially if the legs are folded. The inner row of strong spines in Norellisoma is often hidden by the leg itself in both specimens and photos. However, N. spinimanum has five pairs of strong dorsocentral bristles on the thoracic dorsum whereas Norellia has only two pairs (the two smaller Norellisoma species have three pairs). Since most photos are taken at least somewhat from above, this difference is usually visible and therefore very useful in separating photos of these two species.
This is a not uncommon species in rank grassland and waste places where the adults are predatory. Adults May to August. Irwin (1975)[1] and Speight (1983)[2] record it from Ireland.
World distribution: Palaearctic: Europe: Carpathian Mountains, Andorra, Austria, Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Ireland, Italy, Netherlands, Norway, Poland, Slovakia, Spain, Sweden, Switzerland, Ukraine; Russia: European and eastern Palaearctic; Nearctic: Canada, USA.
References
- , 1975. Recent records of dung-flies (Diptera, Scathophagidae) from Northern Ireland. Irish Naturalists Journal, 18, pp.188-189.
- , 1983. Cordilura aemula and Microprosopa pallidicauda new to Ireland, Trichopalpus fraternus confirmed as an Irish insect and other Irish records of Scathophagidae (Diptera). Irish Naturalists Journal, 21, pp.165-167.