ROBBER FLIES OF THE WORLD 



547 



Genus Rhadiurgus Loew 



FiQUEES 309, 779, 1620, 1621, 2310, 2329, 2864, 2379 



Rhadiurgus Loew, Linnaea Entomologica, vol. 4, p. 133, 1849. 

 T.ype of genus: Asilus variaMlis Zetterstedt, 1838, by mono- 

 typy. 



Flies characterized by the prominent, gibbous face 

 which is polished, sliining black over the middle part 

 of the face. General appearance rather like Machimus 

 Loew. Bristles absent along the posterior margin of 

 the abdominal tergites but dorsocentral bristles are 

 present posteriorly on the mesonotum. Metanotal cal- 

 losity pilose. Occipital bristles strong. The antenna 

 has a microsegment and short style. The upper and 

 lower parts of the male terminalia tend to be divergent. 

 Length 15 mm. 



Head, lateral aspect : The face in profile is very short 

 on the upper tliird and scarcely visible but rather rapid- 

 ly expands to a large, conspicuous, rounded gibbosity. 

 Eye anteriorly recessive on the lower fifth. The oc- 

 ciput is thick and well developed and extends undimin- 

 ished to the vertex ; its pile is long and fine and com- 

 posed of several rows on the upper and middle portion 

 and becomes longer, more abundant and almost bushy 

 on the lower portion of the occiput and still longer 

 medial to the eye margin. Bristles begin below the 

 middle of the head and consist of 15 pairs, of which 

 the uppermost 5 lie behind the vertex closely adjacent 

 to one another and are exceptionally stout, though 

 rather short and straight or barely curved. Proboscis 

 small, slender, cylindrical, with obtuse apex bearing a 

 few, stiff hairs directed away from the tip; the base 

 below has a number of long, fine hairs and is slightly 

 and gradually swollen when idewed from above; it is 

 slightly compressed dorsoventrally, and there is a high, 

 dorsal ridge. Palpus of one segment bearing nimierous, 

 long, stiff hairs, except medially. The antemia is at- 

 tached at the upper third of head and is of moderate 

 length but slender; the first segment is a little more 

 than twice as long as the second. The third segment 

 is slender, subcylindrical and slightly longer than the 

 combined length of the first two segments; it has a 

 short microsegment, the thick style is barely more than 

 half as long as the third segment and bears an apical 

 spine. Pile of first segment composed of stiff setae, 

 long ventrally with a single, rather long, moderately 

 stout bristle; second segment with a few setae above 

 and below ; third segment with 1 or 2 setae dorsally. 



Head, anterior aspect : The face below the antenna is 

 more than a fifth the width of the head and divergent 

 below. Subepistomal area large, oblique, nearly plane, 

 bare and with a flared ridge on either side. Face micro- 

 pubescent only laterally and across the entire ventral 

 half, leaving a large bare spot above ; there are a few 

 bristly hairs only along the lower lateral margin. 

 Whole middle of face upon the gibbosity with a tri- 

 angular patch of numerous, stout, long, strongly curved 

 bristles, the upper elements, black, directed outward 

 and downward ; the middle and lower elements, white. 



are directed obliquely downward; about 40 or 50 

 bristles present altogether. Front slightly divergent, 

 the vertex slightly convergent; front bare, except later- 

 ally and with a lateral band of about 10 slender bristles. 

 Vertex moderately excavated with slanting sides ; ocel- 

 larium large with 6 or 7 pairs of moderately stout 

 bristles. Eyes with central facets enlarged. 



Thorax : The mesonotum and pleuron poUinose ; pile 

 of mesonotum fine, basally stout, subappressed and 

 setate ; the acrostical setae lie in 2 or 3 rows followed 

 by a bare stripe. Dorosolateral area undifferentiated 

 anteriorly but at the notopleural level are 9 moderately 

 long, stout bristles on each side. Humerus pilose. 

 Lateral mesonotal bristles long and stout, consisting of 

 2 notopleural, 1 postsupraalar, 1 suprapostalar, 2 to 4 

 postalar and 2 pairs of scutellar bristles. Scutellar disc 

 thick, convex, with impressed rim and with a few, 

 slender, erect, bristly hairs. Propleuron with scattered, 

 long, stiff pile ; pronotum with 5 pairs of stout, sharp, 

 moderately long bristles. Upper mesopleuron only 

 with a few, scattered, fine hairs. Upper stemopleuron 

 with 10 or 12 scattered hairs ; upper pteropleuron with 

 a few hairs; posthypopleuron with 2 or 3 fine, long, 

 erect hairs; metapleuron with 4 or 5 slender bristles. 

 Metanotal slopes and the metasternum with pile; post- 

 metacoxal area membranous; tegula pubescent only; 

 squama with a multiple fringe. 



Legs : Anterior and middle femora stout and slightly 

 thickened, the lower margin of the middle femur plane. 

 Middle femur with 2 stout bristles anteriorly and 1 

 other at the apex, 2 at the apex posteriorly and 4 or 5 

 weak, slender bristles ventrally. Middle tibia with 2 

 anterodorsal, 2 dorsal, 4 posterior, 2 posteroventral 

 and 2 ventral bristles. Anterior femur with 2 stout, 

 long, sharp, curved, oblique bristles posterodorsally in 

 the middle, 1 anteriorly at apex and a ventral fringe of 

 12 to 14 fine, long, bristly hairs. Anterior tibia with 

 5 or 6 short dorsal, 3 or 4 very slender posterior and 2 

 long, stout, posteroventral bristles; apex with 12 bris- 

 tles. Tarsi end in large, thin pulvilli with distinct, 

 double ribs; empodium two-thirds as long as claw; 

 claws slender, sliarp, curved at the base. 



Wings: The wings are hyaline, the marginal cell 

 closed and stalked; the anterior branch of the third 

 vein ends close to or at the wing apex; the second sub- 

 marginal cell is slightly narrowed across the middle. 

 First posterior cell narrowed by the base of the second 

 posterior cell and the base of the second submarginal 

 cell. Fourth posterior cell closed and stalked; lower 

 end of discal cell pulled back toward the base ; fourth 

 p^terior cell only slightly convex anteriorly, anal cell 

 closed ; second basal cell ends in three veins, the middle 

 vein short. Marginal and submarginal cells rather 

 wide, but the costa not expanded. Alula large, ambient 

 vein complete. 



Abdomen : The abdomen is cylindrical and slightly 

 tapered ; the sides of first tergite strongly swollen and 

 convex ; abdomen slightly longer than the wings ; Eight 

 tergites present in the male, the eighth about half as 



