Mydas Fabricius

J. Wilcox & N. Papavero, 1971, The American Genera of Mydidae (Diptera), with the Description of three new Genera and two new Species, Arquivos de Zoologia 21 (2), pp. 41-119 : 95-98

Genus Mydas Fabricius

Mydas Fabricius, 1794: 252 . Type-species, Musca clavata Drury (La­ treille, 1810: 443).

Head in anterior view about one and one-half times as broad as high; face at the antennae about three-eighths to nearly one-half width of head; oral margin located opposite lower eye margin; gibbosity about as broad as long. Stem of proboscis subequal to length of oral cavity, labella attached to apical one-half or more and extending out at about a 90 0 angle (Fig. 10), palpi short, about as broad as long. Antennal segment 1 cylindrical and about two times as long as broad; 2 about as long as broad; 3 slender and about four times as long as 1-2; club about four-fifths as long as 3 but in some species less swollen and subequal in length to 3 (Figs. 22-26).

Mesonotum usually with short hairs on lateral margins and dorsocentral stripes; usually bare of pollen but at times these areas densely pollinose. Scutellum usually bare but with a few hairs on the arms. Postscutellum rugose, bare to densely pollinose, without hairs. Pleura pilose on the episternum-1, pteropleura, and metasternum.

Abdominal tergite-1a tuberculate and bare; 1p usually long pilose; remaining segments with short recumbent hairs usually sparse but at times dense; bullae (Fig. 50) variable, usually narrow and from two to four times as long as broad. Sternites 2-7 with recumbent hairs, sparse to quite numerous, usually more numerous on apical segments; more numerous and semi-erect on sternite 8, a 8 about one-half length of 7. Female segments 7 to 9 becoming progressively narrower, with short recumbent hairs directed posteriorly, tergite 8 narrower at apex than at base and posterior margin with a semicircular sunken or membraneous area; apex with a few long hairs. Male genitalia (Figs. 99-101): hypandrium completely coalescent with the basistyli, the resulting structure capsule-like as in Messiasia } but the lateral apodemes undergo a series of transformations, leading to increasing degrees of complexity in their structures; the epandrial halves are united at base and subtrapezoidal in - most species, with a lateral beak pointed outwards in some species; the cerci are comparatively short and are coalescent at the base (Figs. 102-112). (See also d'Andretta, 1951: pl. 9, p. 35; pl. 10, p. 39; pl. 11, p. 41; pl. 12, p. 45).

Fore and middle legs usually slender. Hind femora usually strongly swollen but quite slender in a few species; venter with 12 or more short tuberculate spines; hairs variable. Hind tibiae usually with a strong apical spur, at times curved and two times width of hind metatarsus, usually longer than width of the metatarsus but in a few females it is reduced in size and d'Andretta (1951) reported one species without a spur; there is usually a wide ventral keel but in a few species it is very narrow. Hind metatarsus from two to three times as long as broad and shorter than to subequal to the length of 2-3.

Alulae with a dense fringe of squamose hairs. Wings narrow to quite broad; second submarginal cell closed and short petiolate; first posterior cell broadly open; posterior crossvein usually present, atrophied or absent in a few species; axillary lobe about as broad as long; ambient vein complete.

Length, 15-60 mm.

Geographic range: Canada to southern South America (but not found in Chile).

An extremely varied genus. The most consistent characters are the form of the proboscis and the location of the oral margin opposite the lower eye margin. These are also characters of Phyllomydas Bigot , but its broad face and gibbosity, and its unique female terminalia, separates it quite readily from Mydas .