Taxonomy
Cheilosia grossa
Distribution
Species Biology
Preferred environment
Deciduous forest/open ground; clearings and tracksides in woodland and scrub; poorly drained pasture. The distribution and frequency of C. grossa do not reflect the ubiquity and abundance in Ireland of the known larval host plants. Whatever ecological factors determine the success of C. grossa, superficially at least it would seem very unlikely that availability of larval food supply - various thistles, notably Carduus and Cirsium spp.- is one of them. However, most plants have defences against being consumed and it remains possible that C. grossa is unable to use more than a small proportion of the population of apparent appropriate plant hosts because of their physiological condition - i.e. perhaps C. grossa requires plants in poor condition if its larvae are to gain access. The potential of C. grossa to act as an agent of biological control of thistles has been investigated (Rizza et al, 1988), but this does not seem to have led to any explanation for the disparity between the distribution and numbers of C. grossa and of its potential plant hosts. In Ireland, the adults of C. grossa are most frequently encountered in woodland or scrub-invaded pasture situations, where the larval host plants may not be particularly obvious and it is possible that availability of early-blooming flowers required by the adults is to some extent dictating where this hoverfly can maintain populations.
Adult habitat & habits
Males hover at from 2 - 10 metres, usually beside bushes or hedges in sheltered situations; females fly fast and low over ground vegetation in clearings and along tracks; both sexes visit flowers of low-growing plants and trees, usually towards the middle of the day. Although the known food plant of the larva of this species is typically a pasture plant, most records of the adult insect are from sheltered woodland sites, not open country. The early season at which C. grossa is in flight may dictate that this species occurs only where woodland and pasture are closely interdigitated, the larvae requiring the pasture for appropriate host plants, the adults requiring the woodland for its early flowers.
Flight period
March/April, and May at higher altitudes. Larva: described and figured by Rotheray (1988a, 1994), miner in stems of Cirsium spp. (Rotheray, l.c.) and Carduus spp. (Dusek and Laska, 1962); detailed information about larval biology is provided by Rizza et al (1988), who use the name C. corydon (Harris) for this species. This species overwinters as a puparium.
Flowers visited
Anemone nemorosa, Corylus, Prunus spinosa, Ranunculus spp., male Salix, Taraxacum, Tussilago.
Irish reference specimens
In the collections of NMI and UM
Determination
Haarto and Kerppola (2007a), van der Goot (1981), Violovitsh (1986). The surstyli of the male terminalia are figured by Stubbs and Falk (2002) and Violovitsh (1986). The adult insect is illustrated in colour by Bartsch et al (2009b), Stubbs and Falk (1983) and Torp (1984, 1994). Some authors, like Rizza et al (1988) have used the Harris name corydon for this species. However, neither figure nor original description of corydon can be applied unambiguously to this species, there is no Harris type material of corydon in existence and no neotype has been designated. Under these circumstances there is no clear basis for application of the name corydon and it is thus not used here.
Distribution
World distribution(GBIF)
Fennoscandia south to Spain; Ireland eastwards through northern, central and southern Europe into Asiatic parts of Russia in Siberia. Also recorded from the Oriental region (Uttah Pradesh in northern India) and N Africa (Morocco). It is widely distributed in continental Europe, though records are few, and extends beyond Europe into Siberia and south east as far as northern India. This species is probably to some extent under-recorded everywhere, due to its early flight season.
Irish distribution
Recorded from Ireland in Coe (1953). C. grossa is sparsely, but widely, recorded in Ireland. It is not threatened in Ireland, and unlikely to become threatened while thistles are omnipresent in the countryside.
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.