Microdon Explained

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 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.^{[1] [2]}

Appearance

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.^[1]

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.^[3] They are slow-moving. Most have the spiracles on a peg-like protuberance extending from the end of their abdomens.

Behaviour

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,^[3] others are speculated to be scavengers.^[4] 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 life cycles, biological information on most species is limited.

Species

Microdon is divided into six subgenera (including Microdon sensu stricto), plus five species groups and some unplaced species in Microdon sensu lato.

Subgenus Chymophila

See main article: Chymophila.

Nearctic:

• Microdon fulgens Wiedemann, 1830 (Synonyms: Microdon euglossoides Gray, 1832; Chymophila splendens Macquart, 1834)

Neotropical:

Oriental:Palaearctic:

• Microdon katsurai Maruyama & Hironaga, 2004^[5]

Subgenus Dimeraspis

• Microdon abditus Thompson, 1981
• Microdon adventitius Thompson, 1981 ^[6]
• Microdon fuscipennis (Macquart, 1834)
• Microdon globosus (Fabricius, 1805)^[7]
• Microdon marmoratum Bigot, 1884 ^[8]
• Microdon remotus Knab, 1917^[9]

Subgenus Megodon

See main article: Megodon.

• M. planitarsus Keiser, 1971
• M. stuckenbergi (Keiser, 1971)

Subgenus Microdon sensu stricto

Nearctic

Neotropical

Oriental:

Palaearctic

Subgenus Myiacerapis

See main article: Myiacerapis.

Myiacerapis is a subgenus of the hoverfly genus Microdon. It contains only one species, Microdon villosus.^{[10] [11]} It is native to Uganda, though an undescribed species is known from South Africa.^[10] Larvae are found in ant nests.

Subgenus Syrphipogon

See main article: Syrphipogon. There are two species described in Syrphipogon:^[10]

• M. fucatissimus (Hull, 1937)
• M. gaigei Steyskal, 1953

Microdon sensu lato species groups

craigheadii-group

Nearctic:

• Microdon craigheadii Walton, 1912

erythros-group

Afrotropical

• Microdon erythros Bezzi, 1908

= Microdon erytherus Bezzi, 1921 (misspelling)

• Microdon luteiventris Bezzi, 1915

mirabilis-group

Neotropical

• Microdon bertonii Bezzi, 1910

= Microdon arcuata Curran, 1941

• Microdon iheringi Bezzi, 1910
• Microdon mirabilis Williston, 1888

tarsalis-group

Afrotropical:

• Microdon tarsalis Hervé-Bazin, 1913

= Microdon bequaerti Curran, 1929

Unplaced species

Afrotropical

• Microdon harinhalai (Reemer, 2015) ^[12]
• Microdon berobak (Reemer, 2015) ^[12]
• Microdon ifanadiana (Reemer, 2015) ^[12]
• Microdon irwini (Reemer, 2015) ^[12]
• Microdon janne (Reemer, 2015) ^[12]
• Microdon sava (Reemer, 2015) ^[12]
• Microdon tsara Keiser, 1971

Australian / Oceanian:

• Microdon amabilis Ferguson, 1926
• Microdon macquariensis Ferguson, 1926
• Microdon nigromarginalis Curran & Bryan, 1926
• Microdon pictipennis (Macquart, 1850)

= Microdon pictulipennis Hull, 1944

• Microdon rieki Paramonov, 1957
• Microdon waterhousei Ferguson, 1926

Oriental:

• Microdon carbonarius Brunetti, 1923
• Microdon pagdeni Curran, 1942
• Microdon trimacula Curran, 1928
• Microdon unicolor Brunetti, 1915

Notes and References

1. 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 . Zootaxa . 1879 . 21–48 . Magnolia Press . New Zealand . 10.11646/zootaxa.1879.1.3 . 1175-5334 . 2009-09-11 . free .
2. Thompson . F.C . 1981 . Revisionary notes on Nearctic Microdon flies (Diptera: Syrphidae) . Proceedings of the Entomological Society of Washington . 83 . 725–758 . Allen Press . Washington D.C. . 0013-8797 .
3. 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 . 83 . 716–724 . Allen Press . Washington D.C. . 0013-8797 .
4. Book: Donisthorpe, H. St. J. . 1927 . The guests of British ants : their habits and life-histories . London . Routledge . 244 .
5. 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) . Bulletin of the National Science Museum . 30 . 4 . 173–179 . National Science Museum, Tokyo . Tokyo .
6. Thompson . F.C . 1981 . Revisionary notes on Nearctic Microdon flies (Diptera: Syrphidae) . Proceedings of the Entomological Society of Washington . 83 . 725–758 .
7. Book: Fabricius, Johann Christian . 1805 . Systema antliatorum : secundum ordines, genera, species, adiectis synonymis, locis, observationibus, descriptionibus . Brunsvigae . 372 . ?
8. Bigot . Jacques-Marie-Frangile . Diptères nouveaux ou peu connus. 22e partie, XXXII: Syrphidi (2e partie). espèces nouvelles, No 1er . Annales de la Société Entomologique de France . 1884 . 3 . 6 . 315–356 . 24 July 2021.
9. Knab . F. . 1917 . On some North American species of Microdon (Diptera: Syrphidae) . Proceedings of the Biological Society of Washington . 30 . 133–143 .
10. Menno . Reemer. Gunilla. Ståhls. 2013. Generic revision and species classification of the Microdontinae (Diptera, Syrphidae). ZooKeys. 288. 1–213. 10.3897/zookeys.288.4095. 23798897. 3690914. free . 2013ZooK..288....1R .
11. 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 . Zootaxa . 1879 . 21–48 . Magnolia Press . New Zealand . 10.11646/zootaxa.1879.1.3 . 1175-5334 . 2009-09-11 . free .
12. Reemer . Menno . 2015 . Six new species of Microdon Meigen from Madagascar . Zootaxa . 4034 . 1 . 127–147 . 10.11646/zootaxa.4034.1.6 . 26624434 . 44650485 .