DASyPOCONINAB 



ROBBER FLIES OF THE WORLD 



157 



8 short, stiff bristles. Anterior eye facets rather 

 strongly enlarged. 



Thorax: The thorax is characteristically pollinose, 

 the mesonotum long, gently convex. Pile of mesono- 

 tum short over the middle, fine, nearly erect and setate, 

 and becoming slightly longer and coarse laterally. 

 Acrostical bristles not differentiated; dorsocentral 

 bristles a little longer and stouter in front of the scutel- 

 lum. Humerus with fine, long, erect pile only, or with 

 numerous, minute, very stout setae, or with as many as 

 6 stout, moderately long bristles. Lateral mesonotal 

 bristles present as follows: 3 notopleural with some- 

 times additional bristles anterior to these or covering 

 the entire presutural border, or with a single post- 

 humeral bristle; supraalar usually with 1, sometimes 3 

 or 4, 2 in the type of genus ; postalar with 3 or 4 and 

 sometimes fewer; scutellar margin with 2 to 4 pairs. 

 Disc of scutellum convex, pollinose, with sometimes a 

 few, fine hairs. Anterior propleuron ventrally with 

 thick tufts of long, fine pile in many species. The post- 

 propleuron usually with 1 or 2 more stout, long bristles, 

 or with only minute, short setae. Pronotum with fine 

 or stiff pile or frequently with slender bristles. Pos- 

 terior and anterior sternopleuron, pteropleuron, pos- 

 terior hypopleuron, and the posterior mesopleuron with 

 fine pile; mesopleuron sometimes with a few fine 

 bristles. Pteropleuron sometimes with a rather long, 

 stout bristle. Metapleuron with a narrow, vertical 

 band of stout bristles which may be reduced to 4 or 5 

 or may consist of a wide patch of very long, slender 

 bristles. Metanotal slopes characteristically with a 

 conspicuous patch of stout or slender bristles and stiff 

 pile, rarely reduced to as few as 2 or 3 elements. 

 Lateral and ventral metasternum with fine pile; 

 postmetacoxal area membranous; tegula with bristles; 

 anterior basalare always with bristles and sometimes 

 with a long stout bristle. Presternum fully dis- 

 sociated. 



Legs : The legs are comparatively slender, the femur 

 and tibia comparatively elongate ; their pile is abundant 

 but fine, short and appressed or if a little longer, still 

 appressed. The following complement of bristles 

 present in the type of genus : on the hind femur 5 short, 

 lateral and 6 or 7 short medial, 1 near the apex; its 

 tibia has a double dorsal row with 4 in each row but 

 not aligned as pairs and with 6 ventrolateral, 5 ventro- 

 medial, the first 3 short. Middle femur with 5 short 

 anterior, 2 posterior, 1 at the basal third, 1 near the 

 apex, and the anteroventral surface with 7 very short 

 bristles; middle tibia has 5 anterodorsal, 5 or 6 pos- 

 terodorsal, 5 posteroventral and 5 anteroventral; all 

 these bristles are short. Anterior femur with 3 short, 

 basal anterior bristles, 4 or 5 quite short posterior, and 

 a like number of ventral bristles confined to the basal 

 half. The anterior tibial bristles are a little longer 

 and consist of a double dorsal row containing 5 ele- 

 ments, 6 very short posterior, 6 somewhat longer pos- 

 teroventral bristles. This tibia is without apical spine. 



All tarsi end in slender, sharp claws, well developed 

 pulvilli and slender or slightly bladelike empodium. 



Wings: The marginal cell is narrowly open, the 

 second submarginal cell long and slender ; the anterior 

 branch of the third vein ends shortly before the wing 

 apex; the posterior branch is arched backward strongly 

 in most cases but ending only a moderate distance be- 

 hind the wing apex. First posterior cell widely open, 

 or narrowed to one-half the width of its distal section, 

 or uncommonly, it is narrowly closed in the margin. 

 Base of the second posterior cell swollen, sometimes 

 very strongly swollen and bulging backward; the an- 

 terior crossvein is characteristically strongly oblique; 

 the end vein of the discal cell and of the closed and 

 long stalked fourth posterior cell in alignment and 

 approximately parallel to the wing margin, but both 

 veins undulate. Anal cell closed and stalked; alula 

 moderately large; ambient vein complete. 



Abdomen: The abdomen is long, slender, subcylin- 

 drical, a little tapered and a little longer usually than 

 the wings. Pile of abdomen quite short and scanty, 

 generally composed of fine, subappressed setae, which 

 may be appressed on all segments or erect on the last 

 two segments, especially in females. The abdomen is 

 most commonly shining, rarely wholly pollinose, and 

 frequently with conspicuous, pollinose fascia. Sides 

 of first tergite with 3 to 7 stout bristles. In the males 

 seven tergites, the seventh tergite is quite long. In 

 the females eight tergites, the eighth tergite long or 

 sometimes only one-third as long as the seventh. Male 

 terminalia moderately large and fully rotate. The 

 epandrium is not long, but large, either obtuse or 

 acutely produced, fully cleft and divergent from 

 the base with small, enclosed proctiger. The hypan- 

 drium is characteristic in this genus ; it is thick, convex, 

 posteriorly extended, more or less triangular and bears 

 apically and medially a knifelike extension or plate. 

 Gonopod either short or long and tucked in between 

 the dorsal and ventral elements. Females with acan- 

 thophorites and 6 pairs of stout, long spines; ventral 

 plate with the apex V-shaped, compressed and nar- 

 rowly cleft. 



Of this dominant and interesting genus the author 

 had the privilege of studying more than 50 species in 

 the collections of the British Museum (Natural His- 

 tory) . The species are most numerous in South Africa 

 and Madagascar, but are also numerous in southern 

 Asia. From Australia 1 species has been questionably 

 recorded ; 1 is recorded from Mexico, but these flies are 

 absent from South America, and the presence of 3 or 

 4 species in North America of this African and Asian 

 genus is curious. None are recorded from Europe but 

 2 species are recorded from North Africa. They are 

 powerful and aggressive flies. Bromley (1934) has 

 commented interestingly on their habits. 



Distribution: Nearctic: Microstylum galactodes 

 Loew (1866) ; morosum Loew (1872) ; pollens Osten 

 Sacken (1878). 



Neotropical: Microstylum fulvigaster Bigot (1878). 



