Taxonomy
Parasyrphus nigritarsis
Distribution
Species Biology
Preferred environment
Wetland/wet woods; Alnus/Salix/Populus tremula woodland and Alnus viridis scrub up to 2000m in the Alps. An unusual feature of P. nigritarsis is that its larvae feed on those of leaf beetles (Chrysomelidae), rather than greenfly and their allies. But this larval diet does not provide any obvious explanation for the restriction of the species to cool climates and northerly latitudes. The general absence of P. nigritarsis from farmland, where large populations of some potentially-suitable chrysomelid larvae can occur (e.g. Gastrophysa viridula on Rumex), may well be due to farm management practices, though apparently P. nigritarsis larvae can, on occasion be found with G. viridula (Rotheray and Hewitt, 1999). Normal farming practice of topping grassland during the growing season, before seeding of plants like Rumex takes place, could be expected to ensure that any P. nigritarsis larvae present failed to complete their development, converting the fields into a population sink for species like P. nigritarsis. But dense populations of larval chrysomelids can also occur away from farmland in most parts of Ireland, for instance of Phyllodecta species on various Salix species. It can only be assumed that P. nigritarsis is not food-limited in Ireland, but that other factors come into play to restrict its occurrence here. A similar conclusion might be drawn in respect of its occurrence in continental Europe, where P. nigritarsis is equally restricted. The scattered Irish records of P. nigritarsis are from "cold" wet Salix woodland sites with a well-developed tall-herb ground flora, protected from the grazing activities of livestock - for instance along streams in conifer plantations.
Adult habitat & habits
Males hover at from 5m upwards, beside the canopy of trees edging open spaces within woodland, usually close to water, descending precipitously to settle on trackside foliage of trees and shrubs down to within 1m of the ground, the instant the sun disappears behind a cloud; females may be found resting in similar situations or flying around trackside shrubs. In the Alps, males descend to rest on rocks in the sun and both sexes may seek damp mud/sand for drinking purposes, on hot afternoons.
Flight period
End May/end June. Larva: described and figured by Schneider (1953) and illustrated in colour by Rotheray (1994); predatory on the larvae of chrysomelid beetles on trees and shrubs. The species has also been reared from larvae collected with Gastrophysa viridula on Rumex, in farmland (Rotheray and Hewitt, 1999). But it is a moot point whether P. nigritarsis larvae in such a location would under normal conditions ever complete their development - the farming practice of topping grassland to prevent seeding of aggressive weeds like Rumex would be expected to convert a Rumex stand into a population sink for syrphids like P. nigritarsis. Distinguished from larvae of related genera and some other (unspecified) Parasyrphus species in the keys provided by Rotheray (1994).
Flowers visited
Anemone nemorosa, Potentilla erecta, Prunus cerasus, P. spinosus, Ranunculus, Rhododendron aureum, Rubus idaeus, Salix.
Irish reference specimens
In the collections of NMI
Determination
See Key provided in StN Keys volume. The adult insect bears a striking resemblance to Epistrophe or Syrphus species and can be mistaken for these much more widespread insects in the field. The male terminalia are figured by Hippa (1968b) and Vockeroth (1969). The adult insect is illustrated in colour by Stubbs and Falk (1983), Torp (1994) and Bartsch et al (2009a).
Distribution
World distribution(GBIF)
Norway, Sweden and Finland south to Belgium and also in northern Spain (Cordillera Cantabria); from Ireland eastwards through central Europe into Russia and on to the Pacific coast, including Japan; in N America from Alaska to Quebec and south to Washington and Idaho. In continental Europe P.nigritarsis is known from southern Scandinavia to mountainous parts of northern Spain and through central Europe into European parts of Russia and on through Siberia to the Pacific. It is also know in N America. It is an infrequent species in Britain and in central Europe hardly met with other than in montane situations - it is most easily found in association with high altitude Alnus viridis/Salix scrub.
Irish distribution
Added to the Irish list by Speight (1986a). This species is very localised in Ireland and, although found repeatedly in some of the sites from which it is known, has to be regarded as a suitable candidate for inclusion on any listing of insects requiring protection at national level.
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.