Taxonomy
Platycheirus occultus
Distribution
Species Biology
Preferred environment
Wetland; fen and the periphery of raised bog, coastal marsh and dune slacks, humid, seasonally-flooded, unimproved grassland, moorland. In the Alps, apparently only in wetlands with Phragmites, below 1000m, but in Scandinavia occurs to as far north as taiga wetlands (Nielsen, 1998). The impact and implications of climate change for bats P. occultus is a wetland insect, which occurs in Ireland from sea level to above 1000ft., among tall vegetation in fen, marsh and transition mire, seasonally-flooded grassland, dune slacks and around coastal lagoons. It can also be found in blanket bog, along stream and in association with base-rich flushes. It is not a component of forest, suburban or drained grassland habitats and is absent from the standard farm landscape of green fields plus hedges, but can be found in association with wet, open areas within conifer plantation.
Adult habitat & habits
Flies among thick, tall vegetation and is as easily located by use of a sweep net as by direct observation.
Flight period
April to September, with peaks in May/mid-June and mid-July/August. Larva: not described.
Flowers visited
White umbellifers, Carex spp., Salix repens.
Irish reference specimens
In the collections of NMI and UM
Determination
P. occultus is extremely similar to P. angustatus, P. clypeatus, P. europaeus and P. ramsarensis, from which in nearly all cases it may be distinguished using the keys in Speight and Goeldlin (1990). The features used for separation of P. occultus males from males of P. clypeatus in Stubbs (1996) are also helpful. This species is included in the keys provided by van Veen (2004), Haarto and Kerppola (2007a) and Bartsch et al (2009a). The latter authors also provide coloured figures of the adult insect (male and female). The male terminalia are figured by Goeldlin et al (1990). Although the wing membrane is normally entirely covered in microtrichia in P. occultus, in some females a small bare area may be present on the base of the second basal cell. At present it is not always possible to decide whether a female should be consigned to P. occultus or P. clypeatus and additional key characters for separating the females of these two species would be extremely useful. P. occultus is often found on the wing as an adult in the company of P. clypeatus - there are verified records of P.clypeatus from nearly all localities from which P. occultus has been collected in Ireland and Switzerland. The species is illustrated in colour by Torp (1994).
Distribution
World distribution(GBIF)
Not yet adequately known, but now recorded from Norway, Sweden, Finland, the Faroes (Jensen, 2001), Denmark, Ireland, Britain, northern Germany, France (various parts, including the Paris basin, the Alps, Pyrenees, Massif Central and the Vosges), lowland parts of Switzerland, Liechtenstein (the Rhine valley), Spain and northern Italy (Apennines), Serbia, Turkey. It is also frequent in Britain and the Netherlands, but becomes very localised further south and also further north than the southern edge of Norway. It is also localised in the Alps and apparently reaches the southern edge of its range at 1500m in the northern Appenines. It appears to be endemic to Europe, reaching no further east than Liechtenstein, though this may be due to a lack of recent revisions of eastern European syrphid faunas.
Irish distribution
Added to the Irish list by Goeldlin et al (1990). This species was previously confused with other clypeatus-group species in Ireland. P. occultus is predominantly an insect of western parts of Ireland, where it may be common.
Temporal change
Records submitted to Data Centre in 2025
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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.