Taxonomy
Xanthandrus comtus
Distribution
Species Biology
Preferred environment
Forest, deciduous, broad-leaved evergreen and coniferous; Fagus, Quercus, and Pinus forest and scrub.
Adult habitat & habits
Clearings, tracksides etc., especially where there is a thick understorey of shrubs and young trees; settles on foliage of shrubs etc.; males hover at 3 - 5 metres.
Flight period
May/October (April to November in southern Europe), with no clear period of peak occurrence. Larva: described and figured by Dusek and Laska (1967) and illustrated in colour and distinguished from larvae of related genera in the keys provided by Rotheray (1994). The larvae are known to predate aphids and the caterpillars of various small moths (e.g. Tortricidae), both on trees and low-growing plants. They are also recognised predators of the caterpillars of the pine processionary moths (Thaumetopoea pinivora and T. pityocampa).
Flowers visited
Umbellifers; Arbutus unedo, Filipendula, Juncus, Leontodon, Lonicera, Mentha aquatica, Rosa, Rubus, Succisa.
Irish reference specimens
In the collections of NMI and UM
Determination
The male terminalia are figured by Dusek and Laska (1967). The adult insect is illustrated in colour by Stubbs and Falk (1983), Torp (1984, 1994) and van der Goot (1986). The basis for separation of this species from both X. azorensis and X. babyssa is unclear. According to Sack (1928-32) the legs are more extensively darkened in X. comtus than in X. babyssa, but the difference would seem to be more that in X. comtus the pale parts of the legs are usually a dusky, yellow-brown, whereas in X. babyssa the pale parts of the legs are usually yellow. Given that the pale parts of the legs are more yellow in some specimens of X. comtus than in others, and darker in some specimens of X. babyssa than in others (see coloured photo of male and female X. babyssa provided by Smit et al, 2004) using leg colouration to separate these two taxa does not seem very reliable. Sack (1928-32) does not include X. azorensis in his key.
Distribution
World distribution(GBIF)
From the Faroes (Jensen, 2001) and southern Norway south to Iberia; from Ireland eastwards through central and southern Europe to Russia and the Caucasus and on to the Pacific coast; Japan; Formosa.
Irish distribution
Recorded as occurring in Ireland in Coe (1953). Shaw & Rotheray (1990) suggest this species is not resident in the British Isles, but migrates here each year from the continent. X. comtus is not noted for strong migratory behaviour in continental Europe, though the adult insect has on occasion been recorded as apparently engaging in long-distance movements. In continental Europe, the first generation of X. comtus is on the wing in May (and earlier in southern Europe) and were the species resident here records might be expected from then onwards. So, the fact that X. comtus has only regularly been recorded in Ireland from the extreme south-west, from July onwards, perhaps provides circumstantial evidence supporting Shaw & Rotheray (1990). It might seem that a recent record from the beginning of June, in north-west Co.Mayo, would not fit conveniently with this interpretation. But this specimen was caught within an extensive area of habitat with which the species is not associated, namely blanket bog. Only when engaged in long-distance movements would adult syrphids be expected to occur in habitats entirely unsuitable for development of their larvae (unless visiting flowers in a habitat adjacent one in which their larvae may develop - and the Mayo record was far removed from any obvious X. comtus habitat), so the Mayo record could be interpreted as being of a migrant specimen. However, there is also a recent record from young conifer plantation in Kilkenny, in May (Gittings et al. 2005), the species being subsequently recorded from the same locality in June. The Kilkenny locality provides stronger evidence for the existence of a localised resident population and maybe this insect does now maintain itself here? It would be useful to have more comprehensive seasonal occurrence data from localities where it has been found, in order to decide this issue. The only other Irish record away from the south-west is that of Nelson (1990), of a specimen from Fermanagh, collected at the end of July. There seems to be no reason why X. comtus should be unable to overwinter in Ireland, so if it is a non-resident species the explanation probably has to be sought elsewhere. For instance, although the larvae of this syrphid feed on a range of lepidopterous larvae it is possible that in Ireland caterpillar populations do not build up to sufficient density each year to support X. comtus. An equally simple explanation for the Irish distribution data would be that the species is indeed resident in Ireland and, like many other syrphid species at the northern edge of their range, has only one generation per year in Ireland, which is on the wing in June/July. This would certainly fit with the origin of most specimens recorded in Ireland, which are from mature oak woodland in either the Killarney valley or Glengarriff, not from anomalous habitats or locations. The Crom estate in Fermanagh, origin of the record published by Nelson (1990), is also mature oak woodland. In the absence of any serious attempt to resolve this issue the status of X. comtus as a resident species remains open to question. All that can be said of it is that, when found in Ireland, it has normally been in association with oak forest, which is in keeping with its ecology elsewhere. If it is a migrant, it has singularly failed to establish itself in the extensive conifer plantations now scattered around the Irish countryside, despite its equal association with conifer forests in continental Europe. If it is a migrant, there seems to be no explanation for the localisation of records in Killarney and Glengarriff, either. Some of the other migrant species, like Scaeva pyrastri, turn up all round the coast of Ireland, and inland as well. Viewed in this way, it could be argued that X. comtus exhibits characteristics of a relictual, indigenous population in Ireland, rarely moving beyond its remaining, very localised population centres. The few Irish records of X. comtus are from western and northern parts of the island. The species is very localised here and perhaps requires to be regarded as vulnerable to extinction. However, its population centre in the south-west has been known throughout the 20th century and the species can still be found there without difficulty. The fact that it is open to question whether X. comtus is resident there complicates assessment of its conservation status, which might in consequence realistically be regarded as indeterminate. Elsewhere in Europe, X. comtus reaches north only as far as the southern edge of Scandinavia, but becomes frequent further south and in central Europe. It also occurs widely in Asiatic parts of the Palaearctic.
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.