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Classification:

Tropidia scita belongs to the subfamily Eristalinae.

Distribution:

From Fennoscandia south to central France; from Ireland eastwards through central Europe and on through Russia to the Caucasus and in Asia as far as the Pacific coast and Japan.

Habitat:

Moist to wet nutrient-rich biotopes with open waters, almost always near reeds; frequently in swamp forests, at slow flowing waters, in humid, unimproved grassland, also in coastal regions in association with freshwater marsh.

Description:

Body length 7 - 11 mm; wing length 5.5 - 8.25 mm; arista (antennal bristle) glabrous; face with clearly protruding mouth edge; abdomen yellow-black; hind femora thickened with large triangular projection on the underside, shortly before apex.
Female: Hind femora entirely black or black except for a narrowly light apex.
The hind femora of the females of the second European Tropidia species Tropidia fasciata are yellow at the base.

Biology:

Adults of Tropidia scita are found from May to August, with occasional specimens on into September. Little is known about the life of the species. The species probably forms two generations, whereby the smaller 2nd generation probably develops only under favorable conditions.
The adult flies are flower visitors. They were observed on ranunculaceae (Potentilla erecta, Ranunculus), umbelliferae, Cardamine, Corydalis, Euphorbia, Galium, Iris pseudacorus, Myosotis, Rubus, Sorbus aucuparia, Symphytum, Vaccinium and Valeriana.
The larvae probably live and develop in the decaying vegetation at the margins of ponds, ditches and other water bodies. A larva of Tropidia scita was found between the basal leaf sheaths of common bulrush (Typha latifolia). The larvae probably pupate in the litter layer in the reed vegetation.

References, further reading, links:

1. Pape T. & Thompson F.C. (eds) (2017). Systema Dipterorum (version 2.0, Jan 2011). In: Species 2000 & ITIS Catalogue of Life, 2017 Annual Checklist (Roskov Y., Abucay L., Orrell T., Nicolson D., Bailly N., Kirk P.M., Bourgoin T., DeWalt R.E., Decock W., De Wever A., Nieukerken E. van, Zarucchi J., Penev L., eds.). Digital resource at www.catalogueoflife.org/annual-checklist/2017. Species 2000: Naturalis, Leiden, the Netherlands. ISSN 2405-884X.
2. Gerald Bothe: Bestimmungsschlüssel für die Schwebfliegen (Diptera, Syrphidae) Deutschlands und der Niederlande, DJN, 1984, ISBN 3-923376-07-3
3. M.C.D.Speight: Species Accounts of European Syrphidae (Diptera), Glasgow 2011, Syrph the Net, the database of European Syrphidae, vol. 65, 285 pp., Syrph the Net publications, Dublin.
4. Menno Reemer, Willem Renema, Wouter van Steenis, Theo Zeegers, Aat Barendregt, John T. Smit, Mark P. van Veen, Jeroen van Steenis, Laurens van der Leij: De Nederlandse Zweefvliegen (Diptera: Syrphidae), Nederlandse Fauna 8, 2009.
5. Speight, M.C.D. & Sarthou, J.-P. (2014) StN keys for the identification of the European species of various genera of Syrphidae (Diptera) 2014 / Clés StN pour la détermination des espèces Européennes de plusieurs genres des Syrphidae (Diptères) 2014. Syrph the Net, the database of European Syrphidae, Vol. 80, 125 pp, Syrph the Net publications, Dublin
6. Graham E. Rotheray: Colour Guide to Hoverfly Larvae (Diptera, Syrphidae) in Britain and Europe, Dipterists Digest No.9, 1993, Derek Whiteley, Sheffield, England, ISSN 0853 7260