s.s. mutabilis (Linnaeus, 1758):592

Microdon is the nominotypic group, hence, remains some what a catch all for various unrelated species not placed in other genera. The species related to the type, mutabilis Linnaeus, are restricted to the North Temperate region and are characterized by long antenna, scutellum with apical calcars, vein R4+5 with an appendix, simple legs and abdomen. The European species have been revised (Doczkal & Schmid 1999, Schmid 2004), Nearctic (Thompson 1981b) and Japanese (Maruyama & Hironaga 2004, Hironaga & Maruyama 2004) (from Cheng and Thompson 2008).

From original description (Linnaeus 1758).

M. antennis fetariis elongatis tomentofa, abdomine nigro grifeoque mutabili, scutello ferrugineu, thorace immaculato. Habitat in Europa.

New description:

MALE.

Head: Face straight, without tubercle, concave, shiny black, golden yellow pilose; gena black, golden yellow pilose; frons shiny black, golden yellow pilose; dichoptic, eye bare; vertical triangle shiny black, golden yellow pilose; antenna black, scape elongate, 1.5 times longer than basoflagellomere, basoflagellomere 2 times longer than pedicel; occiput black, broader dorsally, yellow pilose.

Thorax: Scutum shiny black, punctuate, with long, golden yellow pile; postpronotum pilose; scutellum yellowish, dark basally, with two posterior calcars, golden yellow pilose, subscutellar fringe absent. Pleuron black, punctuate, golden yellow pilose; anepisternum pilose, bare medially and ventrally; anterior anepisternum pilose; metasternum bare; calypter yellow; plumula absent; halter yellow; spiracular fringes brownish. Wing: Wing membrane yellowish, entirely microtrichose. Vein R4+5 with a long appendix; vein M1 recessive. Alula broad, microtrichose. Legs: Coxae, trochanter and femora black, yellowish pilose; tibiae and tarsi orange, yellowish pilose except basal half of tibiae white pilose. Meta basitarsomere slightly broadened.

Abdomen: Oval, narrowed posteriorly, concave, unmargined. Dorsum black, with white, appressed pile except terga 3 and 4 black pilose anteriorly and medially. Genitalia orange.

Microdon (Microdon) mutabilis (Linnaeus, 1758).

Linnaeus, C. (1758) Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Ed. 10, Vol. 1. 824 pp. L. Salvii, Holmiae [= Stockholm]. [1758.01.01]

Synonyms:

Parmula cocciformis Heyden, 1825: 589.

Scutelligera ammerlandia Spix, 1824: 124.

Microdon rhenanus Andries, 1912: 307.

Musca viridescens Villers, 1789: 463.

Musca mutabilis Linnaeus, 1758: 592.

Aphritis apiarius Latreille, 1804: 193.

Musca apiformis De Geer, 1776: 128.

Aphritis auropubescens Latreille, 1805: 358.

Microdon latipes Curtis, 1837: 249.

Musca nova Schrank, 1776: 93.

Microdon scutellatus Schummel, 1841: 116.

Syrphus apiformis Rossi, 1790: 287.

Microdon auricomos Fabricius, 1805: 184.

Mulio apiarius Meigen, 1805: 185.

Microdon mutabilis is very similar to M. myrmicae and they can only be differentiated by larval/pupal characters and on the base of the host ant: Formica lemani in Microdon mutabilis; Myrmica scabrinodis (and maybe other Myrmica species?) in Microdon myrmicae .

This species may be distinguished from other European species except M. myrmicae using the keys provided by Doczkal & Schmid (1999). At present M. mutabilis is only reliably distinguished from M. myrmicae by features of the puparium. Schönrogge et al. (2002a) confine application of the name mutabilis to specimens bred from nests of the ant Formica lemani on well-drained (i.e. non-wetland) sites. Since there is no way to know which ant host was used by specimens of M. mutabilis collected as adults, this restriction of the name renders such specimens unidentifiable, unless they have a body length greater than 10 mm, that being the greatest size known to be reached by M. myrmicae. The orange colour of the scutellum, often found in M. mutabilis, has been referred to in keys as diagnostic, the scutellum being black/bronze in the other European species. Unfortunately, this is not a reliable feature and specimens of M. mutabilis (and M. myrmicae) can be found in which the scutellum is entirely bronze, with no trace of orange colouration. This is particularly true of M. mutabilis specimens reared from nests of Formica lemani. Speight (2003b) points out that the morphology of the larval mouthparts suggests that M. rhenanus Andries, synonymised with M. mutabilis (L.) by Doczkal & Schmid (1999), may well not be the same species as M. mutabilis sensu Schönrogge et al. and requires reassessment. The appearance of the adult insect is indicated by the coloured figures of "M. mutabilis" in Bartsch et al. (2009b), Kormann (1988), Stubbs and Falk (1983), Torp (1984, 1994) and van der Goot (1986) (from Speight 2010).

There are no definite records of this insect visiting flowers for feeding purposes, but Delforge (1994) states that the flowers of the orchid Ophrys fuciflora are known to be visited by this species, presumably by male flies attempting copulation, since the flowers have a strong resemblance to Microdon species and various species of the genus Ophrys employ the technique of attracting particular insects to attempt copulation, as a mechanism for ensuring pollination, the pollinia becoming attached to the insect during its exertions and then getting transferred to another flower in subsequent false-mating attempts (Speigth 2010).

The distinctive almost slug-like larvae of these species live in ants nests. They are hemispherical in shape, heavily armoured and believed prey on the eggs and larvae of a number of ant species, including Lasius sp., Formica lemani and Formica fusca.

Adults fly between May and July in Europe.

Microdon mutabilis is supposedly occurring from Fennoscandia south to Iberia and the Mediterranean; from Ireland east through most of Europe, into European parts of Russia; through Siberia to the Pacific coast. But existing range data for this taxon must now be regarded as unreliable, since they are based almost exclusively on specimens collected as adults that were determined prior to description of M. myrmicae. The only records of Microdon mutabilis sensu Schönrogge et al (2002a, b) given by those
authors are from Britain and Ireland. Re-appraisal of the range of M. mutabilis is now required, based on bred material for which diagnostic puparial features can be examined. Reemer et al (2009) no longer regard M. mutabilis as present in the Netherlands (Speight 2010).

Adults of this species usually fly low over ground vegetation, in woodland clearings and along woodland paths, or out in open pasture; males hover at 1 - 3m in clearings etc.; frequently settles on stones or bare ground (Speight 2010).

Preferred adults' environment: open ground; sparsely-vegetated, dry, rocky ground with loose stones
appropriate for ants nests; heathland; ancient, unimproved pasture and grassy clearings in forest, where
long-established ants' nests are present (Speight 2010).

Adults emerging from puparia collected from nests of Formica species are generally larger than adults emerging from puparia collected from nests of Lasius species.