Fabricius, J.C. (1798) Supplementum entomologiae systematicae.  + 572 pp. C. G. Proft et Storch, Hafniae [= Copenhagen]. [1798.05.20]
Spazigaster ambulans (Fabricius)
Following Gharali and Reemer (2010), the genus Spazigaster is separated from other genera in the subfamily Syrphinae by the combination of the following characters: black face and scutellum; antenna shorter than head; arista plumose (hairs more than twice as long as aristal width); calypter bare; anepisternum bare; katepisternum with pile patches widely separated; metasternum entire (not reduced); male metatibia with concave depression; abdomen elongate and petiolate (obvious in female, less obvious in male) with tergum 2 narrower than tergum 3; terga without marginal sulcus.
Spazigaster ambulans is similar to S. nostra, but differs by having pile on face, scutum and scutellum completely pale (mostly black in nostra); metaleg in male with deep emargination (about as deep as width of tibia at level of emargination) (Gharali and Reemer 2010).
Head: Face with distinct facial tubercle, not produced forward, black, slightly silvery pollinose laterally, black pilose; gena black, yellowish white pilose; frontal triangle black, black pilose; vertical triangle black, black pilose; antenna shorter than head, black to dark brown, arista plumose (hairs more than twice as long as aristal width); eye bare, dichoptic; occiput black, withish-yellow pilose on ventral 1/2, black pilose on dorsal 1/2.
Thorax: Scutum and scutellum black, punctuate, golden yellow pilose; postpronotum bare; subscutellar fringe complete with golden yellow pile. Pleuron black, golden pilose except anterior anepisternum, katatergum, metepisternum bare; katepisternum with pile patches widely separated; metasternum entire (not reduced), bare; calypter brownish yellow; plumula white; halter yellow, stem a bit darker; spiracular fringes brown. Wing: Wing membrane lightly brown, microtrichose. Alula broad, microtrichose. Legs: dark brown, femora yellow pilose, the rest black pilose; metatibia with concave depression.
Abdomen: terga without marginal sulcus; abdomen elongate and petiolate (obvious in female, less obvious in male) with tergum 2 narrower than tergum 3, dark brown, yellow pilose on 1st, 2nd, 3rd and anterior half of 4th terga, black pilose posteriorly; sterna dark brown, pale pilose.
Similar to male except for normal sexual dimorphism and as follows: frons black with two lateral silvery pollinose maculae, black pilose; occiput more pale pilose; metatibia not modified as in male, but slightly curve or with small concavity in posterior view; abdomen with orange markings: 2nd tergum orange with medial black macula not reaching lateral margins on anerior margin; 3rd tergum orange; 4th tergum black posteriorly with orange fascia on anterior margin broadening laterally.
GenBank accession number for this species are: protein-coding COI gene (EF127350) and rRNA 28S gene (EF127431).
In life, the abdomen of both the male and female may be orange, dull in the male, but shining in the female. The male may also be almost entirely black in life. Once dead, the orange colouration fades almost completely in the male, which then always appears unicolourous black, while the female retains its orange abdomen (Speight 2010).
Sack (1932), in his review of Palaearctic Syrphidae, placed this genus in the subfamily Bacchinae. Dušek and Láska (1967) considered it as a member of the tribe Melanostomini. Shatalkin (1975) discussed the importance of some morphological characters and divided the tribe Melanostomini into two subtribes, and included Spazigaster in the subtribe Platycheirina. Thompson and Rotheray (1998) considered it as a subgenus of Platycheirus. Recently, Mengual et al. (2008) studied the phylogeny of the subfamily Syrphinae using two genes, mitochondrial COI and nuclear 28S rRNA. Their results supported Shatalkin's idea about Spazigaster and it was recovered as sister group of Syrphocheilosia, being Rohdendorfia sister group of both.
Specimens of S. ambulans were swept in a grassland in northern Iran on the plant Mentha longifolia (L.) Hudson, 1762 (Lamiaceae [=Labiatae]), near a narrow local river (Gharali and Reemer 2010).
Adults visit flowers of Umbelliferae; Salvia, Saxifraga aizoides (Speight 2010).
Flight period for S. ambulans ranges from the end of June to mid August (Speight 2010).
S. ambulans has a wider distribution and occurs from Europe to Transcaucasia and Turkey (Gharali and Reemer 2010).
Adults inhabitat usually along streams. Both sexes fly low with a curious zig-zag flight reminiscent of certain ichneumonids, and on landing run in a hesitant way as do many ichneumons. The males hover at 1-3 metres and descend to rest on foliage of large-leaved bushes (e.g. Alnus viridis) or umbels. Males tend to fly around the edge of stands of bushes, while the female is more secretive, flying within the vegetation (Speight 2010).
Adults' preferred environment: scrub/freshwater edge; Alnus viridis thickets in particular, along seepages and streams in poorly-drained, unimproved, calcareous and non-calcareous alpine and montane grassland to above 2,500 m.; alpine glacier floodplains; can occur in riverside/streamside situations at lower altitudes in the Alps, down to 450 m. (Speight 2010).
Larva of S. ambulans is undescribed. The marked association between this insect and thickets of low, water-side shrubs is a strong indication that Spazigaster larvae inhabit these thickets. It is to be expected that they predate plant bugs, or similar insects, living somewhere in these thickets. However, the larvae could be located mostly on twigs or other woody parts rather than on the foliage and may well have some particular relationship which results in the observed restriction of S.ambulans to higher altitudes/colder locations, within its geographic range (Speight 2010).
Spazigaster ambulans (Fabricius)
The genus Spazigaster was described by Rondani (1843) and has two species, Spazigaster ambulans (Fabricius, 1798) and S. nostra Zimina, 1963.