INTRODUCTION 



ROBBER FLIES OF THE WORLD 



17 



Dasypogon diadema Fabricius as an apparent accom- 

 paniment to courtship. Several dipterists have been in- 

 terested in the relative ease with which robber flies sub- 

 due their prey and accounts are summarized by Melin 

 (1923). Several students have commented on the ra- 

 pidity of the paralysis of the victim after capture, and 

 Bromley (1923) describes the striking ability of 

 Proctcwanthus rufus Williston to reduce a live bee to 

 the status of a mere shell, by extracting nearly all of the 

 digestive, nervous, and muscular systems. It appears to 

 be unknown whether this reduction is aided by a his- 

 tolytic enzyme, but in view of the results accomplished, 

 it appears likely. While insects with extremely hard ex- 

 terior covering like Curculio and Hister are captured by 

 asilids, there is a relationship between the strength of 

 the mouthparts and the capacity of the fly to subdue 

 very hard insects. It has been reported that an asilid 

 attacked unsuccessfully a chrysidid wasp, which, 

 though held for some time by the fly, was eventually 

 loosed and flew away unhurt. 



LARVAL HABITS 



Melin (1923) records the rather unusual egg-laying 

 habit of Dysmachus picipes Meigen, which deposits 

 eggs regularly in the spikelets of an ear of Avena or 

 Dactylus, and this author gives figures of known asilid 

 egg shapes. Apparently, the young larvae, upon 

 hatching, fall to the earth, the fall being retarded by 

 the bristly hairs. Again, he noted Neoitamus cyanu- 

 rus Loew ovipositing in alder buds and strobiles. I 

 once captured a very large species of Bomhom'ma En- 

 derlein, which immediately laid two quite large, pur- 

 plish, very short, oblong eggs. Hardy (1929) records 

 the ovipositing of the curious Nerterhaptomenus 

 morus Hardy. He found that the female repeatedly 

 inserted the slender, thin, apical segments of the ab- 

 domen down small holes made by beetles on the twigs 

 of Acacia trees and that the fly moved from hole to 

 hole feeling with its ovipositor until such a place was 

 located. A captive specimen in the laboratory readily 

 oviposited within the holes of a cork. Kershaw (1912) 

 has shown that at least one Oriental species of Pro- 

 machus Loew deposits its eggs within an ooetheca-like 

 case on grass stems. 



The larvae of many genera live in soil. The larvae 

 of the Laphriini and Andrenosomini usually live in 

 decaying wood in old stumps, or beneath bark. I have 

 seen no record of the larval habits of the Atomosini. 

 The larvae of the asilids have been frequently re- 

 garded as predatory in habit, especially by early writ- 

 ers. Perris (1871) found Laphria gilva Linne asso- 

 ciated with Spondylis buprestoides and Criocephalus 

 rusticus, both beetle larvae, and considered that they 

 were preying on these beetles. Kiley (1870a) found 

 Nerax femoratus Macquart larvae preying more than 

 once on grasshopper eggs. 



Malloch (1917) states that all the larvae of the fam- 

 ily that he has found are predatory, feeding on other 

 insect larvae in soil as white grubs or in decaying 

 wood. Melin discusses the evidence up to the time of 

 1923 with considerable detail. His own observations 

 and experiments are quite to the contrary and he be- 

 lieves that the principal food of asilid larvae is vege- 

 table in character. He presents what seems excellent 

 evidence that asilid larvae subsist on a non-carnivor- 

 ous-type of food. Melin believes that attack or con- 

 sumption of animal food sources such as insect larvae 

 is entirely secondary and sporadic, if indeed it ever 

 actually takes place. While Malloch (1917) and 

 Greene (1918) state that asilid larvae feed on other in- 

 sect larvae, they do not claim to have verified this by 

 direct, personal observation, that is, to have seen asilid 

 larvae initiate the attack and extract the contents from 

 larvae prey. The females of the large group of genera 

 in the Dasypogonini are equipped with circlets of 

 spines on the acanthophorites of the ovipositor and 

 many members of the Asilinae likewise have such ac- 

 cessory structures but of a different pattern; both 

 groups deposit eggs in the soil. 



MIMICRY 



As regards mimicry in this family, it seems less well 

 marked than is found in the Syrphid. flies or butterflies. 

 Melin (1923) does not accept the existence of mimicry 

 in the Asilidae, but in this I believe that he is mistaken. 

 Species exhibiting mimicry increase in hot, humid lati- 

 tudes and may be quite lacking in the temperate lands. 

 Shelf ord (1902) calls attention to a species of Laphria 

 Meigen resembling the Hymenopteron Salius serioco- 

 soma; and also Hyperechia fera Wulp resembling the 

 bee Xylocopa latipes. An African species of Hyper- 

 echia Schiner was noted by Marshall (1902) to closely 

 resemble the bee Xylocopa flavorufa. The Amazonian 

 species of Dasyllis Loew, which resembles bees of the 

 group Eulaema and the various species of Diogmites 

 Loew and Blepharepium Rondani, which resemble some 

 species of wasps, may be considered examples of mimic- 

 ry. The small asilid Megaphorus clausicella Mac- 

 quart from the southern United States is a good mimic 

 of Megachile bees. These examples are generally re- 

 garded as falling in the principle of synaposematic 

 mimicry, or mimicry of aggressive resemblances. Both 

 Shelf ord (1902) and Poulton (1925) have made con- 

 tributions on this subject. Aggressive mimicry favors 

 aggression and offers a measure of protection from cer- 

 tain enemies. Some species produce a loud buzzing 

 sound in flight not unlike some bumblebees. The curi- 

 ous Chilean asilid Lycornya germainii Bigot has for its 

 model the Hymenopteron Elaphroptera scoliaeformis 

 Haliday. 



The American series of mimics from the southwestern 

 states copy the tarantula hunting wasps of the genus 

 Pepsis Fabricius. These noteworthy insects are large, 

 with black or blue-black bodies and wings strikingly 

 colored a yellowish brown. Besides the robber fly Asilus 

 midas Brauer, the series contains Mydas xanthopterus 



