Taxonomy
Xylota tarda
Distribution
Species Biology
Preferred environment
Deciduous forest, Quercus forests (including thermophilous Quercus forest of Q. pubescens), alluvial forest with overmature Populus, brook-floodplain forest and other riparian forests with Populus tremula and Populus plantations. The known association of X. tarda with overmature and dying Populus tremula would not favour this insect in Ireland, where stands of overmature aspen are vanishingly scarce. Aspen does occur in the immediate vicinity of the only known Irish site for X. tarda, hinting that this syrphid may well, indeed, use the rotting wood of this tree as larval microhabitat here. However, in continental Europe X. tarda can be found in an absence of aspen, in particular in oak forest, and its larvae have also been found in rotting wood of overmature beech, so it is possible that it can use other trees in Ireland as well, though the extreme scarcity of X. tarda here would suggest otherwise. In Scandinavia, where aspen is more abundant, so is X. tarda, and its range in Norway extends to the far north of the country, indicating that climatic considerations are unlikely to limit this syrphid in Ireland. X. tarda has to be regarded as an extremely anthropophobic insect in Ireland, unlikely to be found other than with its water-margin habitat.
Adult habitat & habits
Usually in scrub woodland, or open forest with patches of dense scrub, but nearly always on old forest sites; running on foliage of bushes, Rubus etc. at tracksides and edges of clearings and on bare ground; flies through scrub vegetation at 1 - 3 metres from ground.
Flight period
May/August, with a peak at the beginning of July. Larva: described and figured by Rotheray (1991), from larvae collected from a sap run at the base of the trunk of Populus tremula. Rotheray (1994) illustrates the larva in colour. Krivosheina records rearing of this species from larvae collected in rotting wood of Fagus.
Flowers visited
Potentilla, Sambucus.
Irish reference specimens
In the collections of NMI
Determination
See key provided in the StN Keys volume; Bartsch et al (2009b). This species is nearly always found in localities where X. segnis also occurs and is very difficult to distinguish from X. segnis in the field. It is usually seen in much smaller numbers than X. segnis, because of its more secretive behaviour. Despite what is suggested in keys such as those of van der Goot (1981) and Stubbs and Falk (1983), abdominal markings are entirely unreliable as a means of distinguishing X. tarda from X. segnis. The presence of dusting on the anterior parts of the mesopleur and a row of black spines beneath the hind tibiae are diagnostic of X. segnis: these features are absent in X. tarda. The male terminalia are figured by Hippa (1968a). The adult insect is illustrated in colour by Bartsch et al (2009b), Stubbs and Falk (1983) and Torp (1994).
Distribution
World distribution(GBIF)
From northern Fennoscandia south to Spain; from northern Italy (Apennines) and the former Yugoslavia (Slovenia); from Ireland eastwards through central Europe into European parts of Russia; the Caucasus; through Asia to the Pacific coast (Kuril islands). Its status varies from one part of the Atlantic zone to another, but it is apparently threatened in Germany and, in central Europe, it is regarded as threatened in Switzerland. It has a wide range beyond Europe, in Asiatic parts of the Palaearctic.
Irish distribution
Added to the Irish list by Speight et al (1979). Only one locality is known for X. tarda in Ireland and the species has to be regarded as endangered here. It should be included in any listing of insects requiring protection throughout the island.
Temporal change
Records submitted to Data Centre in 2024
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References
Publications
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.