INTRODUCTION 



ROBBER FLIES OF THE WORLD 



by a distinct, padlike, pulvilliform structure or aro- 

 lium ; rarely is a medial appendage of some kind want- 

 ing. Asilids seem to be an early and ancient offshoot 

 from the common stock which gave rise to present day 

 representatives of above mentioned families and which, 

 at a still earlier time, diverged in another direction to 

 produce the families of the Bombyliformia (Bombyli- 

 idae, Cyrtidae, Nemestrinidae) . 



One of the greatest gaps between the Nematocera 

 and the Brachycera lies in the character of the palpus. 

 Palpi of Nematocera are composed of three to five 

 segments; palpi of Brachycera are composed of one 

 or two segments. We have no Brachycera with three 

 palpal segments. Following Williston, 1908, palpi are 

 considered of great significance, and have been ex- 

 amined in each asilid genus. In the lower Dasypo- 

 goninae, in a few generalized types, there is a trace of 

 the antepenultimate segment of the palpus. Williston, 

 1908, gives a summary of past systems of relationships. 



Loew recognized three principal subfamilies of the 

 Asilidae, the Dasypogoninae {Leptogaster Meigen in- 

 cluded), the Laphriinae, and the Asilinae. Schiner 

 (186S) proposed the subfamily Leptogastrinae. Loew 

 emphasized the distinctions of the antennae and wings, 

 and to some extent those of the head, legs, thoracic 

 chaetotaxy, and terminalia. Williston (1908) con- 

 sidered the palpal differences to have more fundamental 

 significance than the state of the marginal cell. Mal- 

 loch (1928) and others pointed out the great diversity 

 of antennal forms within each subfamily. Hermann 

 ( 1920) made a useful subdivision of the Dasypogoninae 

 into three major groups. His divisions, the Prytani- 

 nae, Eremocneminae, and Acanthocneminae, are based 

 on the reduction in the number of visible abdominal 

 segments, and on the presence or absence of the fore- 

 tibial apical spine. Engel (1928) preserved this ar- 

 rangement. Hermami's distinctions, while certainly 

 significant, have the disadvantage of a poor choice of 

 names, since none of them stem from names of genera. 

 For this reason, and because additional tribes have been 

 recognized, Hermann's subdivisions have not been used 

 in this work. 



Among recent schemes of classification, Carrera 

 (1949) followed Hardy (1934) in recognizing only 

 2 subfamilies and placing the Laphriinae with the 

 Dasypogoninae and the Leptogastrinae with the Asi- 

 linae. Bromley, Hermann, Engel, Williston, Me- 

 lander, and Verrall have recognized 4 subfamilies and 

 I believe on good basis. For a basis of recognizing 

 Dasypogoninae, Asilinae and Leptogastrinae, we have 

 fossil records; each of these groups goes back as far 

 as the Miocene. The Asilinae extends into the Oligo- 

 cene and Eocene. No fossil species of Laphriinae are 

 yet known. It may be a relatively Recent subfamily. 

 In the Laphriinae we find 77 genera and about 763 

 species, which occur in all the major world regions. 

 The features shared in common by the Laphystini and 

 the Laphriinae suggest that this subfamily arose from 

 the ancient stock of that tribe. 



Hardy (1948) placed dependence on the relative dis- 

 sociation of the prosternum as a defining character for 

 the higher categories. In some Asilidae the proster- 

 num represents a single or paired, or paired and more 

 or less fused sclerite which is completely isolated by 

 membrane from the lateral propleuron. In others it 

 is solidly fused with the lateral propleuron completely 

 around the anterolateral border of the anterior coxa; 

 this condition is described as a complete or undissoci- 

 ated prosternum. Clements (1951) has shown that 

 there is great instability in the character of the pros- 

 ternum within many groups of asilids. This character 

 seems to have then, in brief, the same defect that the 

 antenna has, in being too variable in this family. Be- 

 cause of the interest attached to it, I have given the 

 condition of the prosternum considerable attention, and 

 have examined its state in a wide variety of lower 

 Brachycera and some Nematocera in an effort to de- 

 cide which condition is the more generalized, the com- 

 plete or the dissociated prosternum. Such a great 

 variety of genera scattered throughout the order have 

 the prosternum dissociated that one might be inclined, 

 because of this very fact, to regard the isolated pre- 

 sternum as the more primitive state for Diptera; but 

 there are certain evidences which suggest that the re- 

 verse is true and which confirm Hardy's conclusion 

 that the complete prosternum is the generalized con- 

 dition. With a dissociated sternum surrounded by 

 membrane, there is made possible a greater flexibility, 

 but less strength because of reduced muscle attach- 

 ment sclerites. Both conditions appear to be desider- 

 ata in a highly predatory group and it seems likely 

 that adaptive factors have entered prominently into 

 the state of the prosternum in various genera of the 

 lower Brachycera. This may account for the lack 

 of a trend in many groups toward the exclusion of the 

 one type or the other. 



Thus, I find that the following genera in other fam- 

 ilies have the prosternum fully dissociated: Rhagio 

 Fabricius, Dialysis Walker, Atherix Meigen, Chrys- 

 opilus Macquart, Symphoromyia Frauenfeld, and Co- 

 enomyia Latreille. But in Solva Walker, on the 

 contrary, the prosternum is complete, well developed, 

 and fused. The prosternum is also dissociated in 

 Culex Linne, Tipula Linne, Exoprosopa Macquart, 

 Eclimus Loew, Syrphus Fabricius, Milesia Latreille, 

 Cochliomyia Townsend, and likewise in all muscoids 

 and higher Diptera which I have examined. 



On the other hand the tabanids, stratiomyids, doli- 

 chopodids, therevids, and empidids, at least generally, 

 have the prostemum fully developed and complete, al- 

 though the first three families named above evidence in 

 common a peculiarity which suggests a relationship 

 and perhaps origin from common stock; this is the 

 curiously broadened state of the prosternum, leaving 

 the anterior coxae far apart. Of the therevids, there is 

 a close resemblance between their prosternum and that 

 of members of the Stichopogonini, where it is also 



