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UNITED STATES NATIONAL MUSEUM BULLETIN 22 4 



curs while in copulation, these parts tend to return to 

 a variable extent to the dorsal position and in the dried 

 cabinet specimens they are usually found in partial and 

 sometimes complete inversion. Probably, in many 

 Dasypogoninae there is permanent rotation, if 

 judgment can be formed from dried material. In the 

 Dasypogoninae, except the Stenopogon Loew group of 

 genera, this male character cannot be used with com- 

 plete confidence because of its variability, nor can it be 

 linked as an associated character with the female char- 

 acter of the spiny acanthophorites in the tribe Dasy- 

 pogonini. Some of the members of the tribe Dasy- 

 pogonini are not rotate, such as Stenopogon Loew and 

 Bathypogon Loew. 



In the lower Dasypogoninae the female terminalia 

 are simple and begin with the ninth segment. If there 

 are fewer segments in the preabdomen than eight, the 

 apparently missing segments can still be found, short- 

 ened, and concealed or partially hidden beneath the 

 last visible segment. In the Dasypogonini and Sticlio- 

 pogonini, the ninth female tergite is subdivided into 

 two lateral plates, the acanthophorites, leaving on each 

 side a quarter-circlet of stout spines which are sharp, 

 blunt or spoon-shaped, and usually consisting of five 

 or more pairs. In the lower Dasypogoninae, as Phel- 

 lus Walker and Dioctria Meigen, and in all the Asilinae 

 this tergite is undivided. 



Immature Stages 



The eggs of asilids vary both in size and shape. 

 They range from very short oval as in Leptogaster 

 Meigen, and Bombomima Enderlein, to medium oval 

 in the case of Laphria Meigen, in which the length of 

 the egg may be twice the width. Melin (1923) figures 

 14 asilid eggs and states that the eggs of Laphria are 

 reddish brown and shiny. The egg he shows of Eutol- 

 mus mfibarbis is nearly four times as long as wide. 

 Eggs of one large species of Bombomima Enderlein 

 are very large, purple in color and short oval. 



Larvae of Asilidae are elongate, tapered at each apex. 

 They tend to be shiny, sometimes furrowed, or with 

 fine stria and with or without dorsal callosities. They 

 possess a clear, distinct head with eleven body seg- 

 ments, which often have rows of minute pores. The 

 terminal segment is divided. The principal spiracles 

 consist of a pair on the prothorax and a pair on the 

 anterior abdominal segment, for which reason they 

 have been regarded in all older writings as amphipneu- 

 stic. Green (1918) found a pair of minute, possibly 

 not functional spiracles on the metathorax, and a pair 

 on the remaining, abdominal segments. The penulti- 

 mate abdominal segment is shorter than the ultimate, 

 distinguishing them from the mydaids, but like them 

 the body is held straight; hairs of ultimate segment 

 not closely approximated as in mydaids. In text-figure 

 6 several typical larvae are shown, after Melin (1923), 

 to whom the interested student is referred for his fine, 

 detailed studies and figures. 



Asilid pupae are of the free and mobile type. 

 Antennal sheaths are present, sometimes divergent, 



situated close to the medial part of eyes. Melin (1923) 

 designates the distinct, thornlike processes, which are 

 found at the base on the one hand, and the distal part 

 of the sheath on the other, as the anterior and posterior 

 processes. Posterior processes generally have three to 

 five teeth. Melin (1923) and Green (1918) both con- 

 sider that the abdomen consists of 8 segments. Dor- 

 sally the segments are provided with a unilinear girdle 

 of spines, which Melin finds change over laterally into 

 bristles, and which Brues and Melander (1932) find 

 alternate as long and short spines. Eight spiracles are 

 generally present. 



More than fifty authors have dealt with the egg, 

 larva, or pupa of Asilidae. As Melin (1923) has 

 pointed out, most of the descriptive and illustrative 

 material, excepting that produced by Malloch (1917) 

 and by Greene (1918), is without comparative value 

 as it goes into entirely too little detail. Many of the 

 observations made on the supposed feeding habits of 

 larvae is of a presumptive or circumstantial character. 

 Melin in his own work states that he had almost a 

 thousand larvae representing many species and not a 

 few genera. Altogether about 50 species have been 

 treated in literature, distributed approximately as fol- 

 lows: Dasypogoninae with 5 genera and 13 species; 

 Asilinae with 17 genera, and 27 species; Laphriinae 

 with 5 genera and 9 species; Leptogastrinae with 2 

 genera and 4 species. Seguy (1932) illustrated a num- 

 ber of larvae and pupae, many from Melin (1923). 

 The bibliographies of Melin (1923), Irwin-Smith 

 (1923), and Henning (1952), should be consulted by 

 those interested in these stages. 



Ecological Relationships 



The majority of species of Asilidae frequent dry and 

 sandy areas, a condition well shown by the greater 

 numbers of species found in arid and semiarid regions ; 

 but even in desert or semidesert country the small 

 drains of dry steam beds attract the greatest number, 

 and sometimes the entire robber fly population of a 

 region will be restricted to such places, which also have 

 the maximum vegetation and the greatest popidation of 

 insects upon which the flies feed. In such country 

 one may often look in vain for Asilidae beyond the 

 banks of the stream bed. In temperate regions a few 

 species occur in wet swamp areas and deep forests. 

 As Bromley (1946) has pointed out, the number of 

 species which occur deep within woods is limited, 

 and these flies tend definitely to concentrate on the 

 edges of woodlands, where shrubs occur and give way 

 to grassland. I spent several weeks at the Canal Zone 

 Biological Area of the Smithsonian Institution, on 

 Barro Colorado Island in Gatun Lake. There in the 

 rain forest never was an Asilid seen within the forest, 

 but several species occurred among the high grass 

 along the edge of clearings. There are species which 

 prefer grasslands, and the plains also have their repre- 

 sentatives. Next to semidesert areas, probably savan- 

 nah country attracts the greatest number. It is said 



