Deciduous forest; alluvial hardwood forest with over-mature trees (especially Populus) and brook-floodplain forest. Two of the Irish records of X. florum are from riparian deciduous forest, in the one case Quercus/Fraxinus, in the other Salix spp. In this general habitat context, the ecology of X. florum in Ireland seems to be as elsewhere in Europe. It is a species associated particularly with alluvial hardwood forest and alluvial brook forest. The third Irish record (Gittings et al, 2005) is from a Fraxinus plantation remote from any stream or river margin and the fourth is from a suburban garden. However, whatever tree the larvae of this species are associated with in Ireland it is not Populus nigra, from which the species has probably been bred elsewhere - Populus nigra is not present at any of the Irish localities for X. florum. Neither is it an indigenous species of tree here. This syrphid has to be regarded as an extremely anthropophobic species in Ireland.
Adult habitat & habits
On trunks and stumps of fallen and felled trees in the sun, in clearings and at tracksides; also on streamside and trackside vegetation in the sun, within woodland.
End May/end July, with most records from June. Dusek and Laska (1960b) described the larva of X. florum from hole-holes in Populus. Their description has been validated as relating to X. florum by Rotheray (2004), who redescribes the developmental stages. Assuming that early records do relate to X. florum, the species has been reared more than once from trunk cavities in Populus nigra. Krivosheina (2001) reports rearing this species from a fallen trunk of Picea.
White umbellifers; Rubus fruticosus.
Irish reference specimens
In the collections of NMI.
See key provided in the StN Keys volume; Bartsch et al (2009b). The male terminalia are figured by Hippa (1968a). X. florum is extremely similar to X. meigeniana (Stack), but in both sexes the antero-dorsal sclerite of the mesopleur (mesoanepisternite 1) is predominantly dull and grey-dusted in X. florum, whereas it is almost entirely undusted and shining black in X. meigeniana. The hypopygium of the male of X. florum is black-haired and the apical margin of the cercus is deeply concave, while in X. meigeniana the hypopygium is predominantly white-haired and the apical margin of the cercus is convex. Also in the male, the hind femora in X. florum carry hairs longer than half the maximum depth of the femur, on the antero-dorsal surface, whereas in X. meigeniana none of the hairs on this part of the hind femora are as long as half the maximum depth of the femur. The 250 females of these two species are more difficult to separate - the infuscation of the wing referred to by some authors, as distinguishing the female of X.meigeniana, can also occur in females of X. florum. Bartsch et al (2009b), Stubbs and Falk (1983) and Torp (1994) figure the adult insect in colour.
From Scandinavia south to central France; from Ireland eastwards through much of Europe into European parts of Russia and the Caucasus and on as far as eastern Siberia. It does not seem to be so threatened elsewhere, and ranges from southern Scandinavia to central France and through central Europe into parts of Asiatic Russia.
Recorded as occurring in Ireland in Coe (1953), but at that time this species was confused with X. jakutorum. The presence of X. florum in Ireland was confirmed by Speight (1976a). X.florum has to be regarded as an endangered species here, and as a candidate for inclusion in any listing of insects requiring protection throughout Ireland.
Records submitted to Data Centre in 2023
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Speight, M. C. D. (2008) Database of Irish Syrphidae (Diptera). Irish Wildlife Manuals, No. 36. National Parks and Wildlife Service. Department of Environment, Heritage and Local Government, Dublin, Ireland.
Speight, M.C.D. (2014) Species accounts of European Syrphidae (Diptera), 2014. Syrph the Net, the database of European Syrphidae, vol. 78, 321 pp., Syrph the Net publications, Dublin.