Hover flies (family Syrphidae) of the genus Microdon are unusual among the Diptera. Like other members of the subfamily, they are myrmecophiles, meaning they inhabit the nests of ants. There are 249 species are known worldwide, with the greatest diversity being from the tropics; 30 species are known from North America, though it is expected that many of these species will be placed in other genera in time, as Microdon has been used as a catch-all for various unrelated species not placed in other genera.
Microdon adults look more or less like typical flies. Like some other hoverflies, they are generally robust and very hairy, often closely resembling bees. They are between 8 and 15 mm long. The antennae are rather long, with the last (third) segment nearly as long as, or sometimes significantly longer than, the first segment; the antennae are nearly as long as the fly's face. These flies are covered in black or pale (white or golden) hairs, and are themselves either black or metallic green or blue. The scutellum is with apical calcars and wing vein R4+5 with an appendix. They have simple legs and abdomens.
The real oddity of the genus Microdon is in its larvae and pupae. These are dome-shaped and look like stout little slugs. Their appearance originally led scientists to describe them as mollusks and scale insects. They are slow-moving. Most have the spiracles on a peg-like protuberance extending from the end of their abdomens.
Adult Microdon flies do not behave like other syrphid flies; they do not hover around flowers, but instead remain very near the ant colonies which serve as larval hosts.
Larvae may be found very deep in ant colonies. Some species actively feed on ant larvae in the colony, others are speculated to be scavengers. Microdon larvae are more or less restricted in their ant host species. Some Microdon species have only ever been found in the colonies of a single ant species, while others are restricted to related ant species or genera. Because these flies have such cryptic lifecycles, biological information on most species is limited.
- Microdon abditus Thompson, 1981
- Microdon abstrusus Thompson, 1981
- Microdon adventitius Thompson, 1981
- Microdon albicomatus Novak, 1977
- Microdon analis (Macquart, 1842)
- Microdon aurulentus (Fabricius, 1805)
- Microdon baliopterus Loew, 1872
- Microdon brunetti Sodhi & Singh, 1991
- Microdon carolae (Capelle, 1956)
- Microdon coarctatus Loew, 1864
- Microdon cothurnatus Bigot, 1883
- Microdon craigheadii Walton, 1912
- Microdon devius (Linnaeus, 1761)
- Microdon diversipilosus Curran, 1925
- Microdon eggeri Mik, 1897
- Microdon fulgens Wiedemann, 1830
- Microdon fuscipennis (Macquart, 1834)
- Microdon globosus (Fabricius, 1805)
- Microdon ignotus Violovitsh, 1976
- Microdon katsurai Maruyama & Hironaga, 2004 
- Microdon laetoides Fabricius, 1935
- Microdon laetus Loew, 1864
- Microdon lanceolatus Adams, 1903
- Microdon lateus Violovitsh, 1976
- Microdon latifrons Loew, 1856
- Microdon manitobensis Curran, 1924
- Microdon maritimus Violovitsh, 1976
- Microdon marmoratum Bigot, 1883
- Microdon megalogaster Snow, 1892
- Microdon miki Doczkal & Schmid 1999
- Microdon mutabilis (Linnaeus 1758 )
- Microdon myrmicae Schönrogge et al., 2002
- Microdon mysa Violovitsh, 1971
- Microdon newcomeri Mann, 1924
- Microdon ocellaris Curran, 1924
- Microdon painteri Hull, 1922
- Microdon pallipennis Curran, 1925
- Microdon piperi Knab, 1917
- Microdon ruficrus Williston, 1887
- Microdon rufipes (Macquart, 1842)
- Microdon scutifer Knab, 1917
- Microdon sophianus Drensky 1934
- Microdon tristis Loew, 1864
- Microdon ursitarsis Stackelberg, 1926
- Microdon viridis Townsend, 1895
- Microdon xanthopilis Towsend, 1895
- Cheng, Xin-Yue; Thompson, F. Christian (2008). "A generic conspectus of the Microdontinae (Diptera: Syrphidae) with the description of two new genera from Africa and China" (PDF). Zootaxa (New Zealand: Magnolia Press) 1879: 21–48. ISSN 1175-5334. Retrieved 2009-09-11.
- Thompson, F.C (1981). "Revisionary notes on Nearctic Microdon flies (Diptera: Syrphidae)". Proceedings of the Entomological Society of Washington (Washington D.C.: Allen Press) 83: 725–758. ISSN 0013-8797.
- Duffield, R.M (1981). "Biology of Microdon fuscipennis (Diptera: Syrphidae) with interpretation of reproductive strategies of Microdon species found north of Mexico". Proceedings of the Entomological Society of Washington (Washington D.C.: Allen Press) 83: 716–724. ISSN 0013-8797.
- Stubbs, Alan E.; Falk, Steven J. (1983). British Hoverflies: An Illustrated Identification Guide. British Entomological & Natural History Society. pp. 253, xvpp.
- Sodhi, N.S.; Singh, A. (1991). "Three new species of family Syrphidae (Diptera) from India.". Acta zoologica cracoviensia. b 34 (1): 315–322.
- Barkalov, A.V. "Syrphidae collection of Siberian Zoological Museum". Novosibirsk, Russia: the Institute of Animal Systematics and Ecology, Siberian Branch of the Russian Academy of Sciences. Archived from the original on October 20, 2008. Retrieved 17 August 2009.
- Maruyama, Munetoshi; Hironaga, Teruhiko (December 22, 2004). "Microdon katsurai, a New Species of Myrmecophilous Hoverfly (Diptera, Syrphidae) from Japan, Associated with Polyrhachis lamellidens (Hymenoptera, Formicidae)" (PDF). Bulletin of the National Science Museum. A (Tokyo: National Science Museum, Tokyo) 30 (4): 173–179.