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Family Asilidae — The Assassin Flies 



Species of moderate to large size, rarely small, usually rather 

 elongate in form, often thickly hairy and always with bristles, entirely 

 predaceous in habit. 



Head flattened, broad and short, separated from the thorax by a 

 neck (the prothorax) and freely movable. Front excavated above, 

 usually broad in both sexes, rarely narrow. Ocelli present, usually 

 situated upon a rounded tubercle; front with bristles. Antenna! por- 

 rect, usually composed of three simple segments, the third more or less 

 elongate and with or without a terminal style or arista, the latter very 

 rarely pectinate, the style rarely strongly thickened and forming one 

 or two additional segments. Proboscis of moderate length, horny and 

 adapted for piercing, directed downward or forward; labellse never 

 fleshy; palpi composed of two segments, the basal one often small and 

 not freely articulated with the second. Thorax variable in shape, con- 

 vex, usually bearing bristles. Abdomen composed of eight segments, 

 the liypopygium and ovipositor usually prominent. Legs strong, usually 

 bristly, of moderate length, the femora often, the posterior tibire some- 

 times thickened, the legs sometimes very long and rather slender; 

 empodium present or absent; the puvilli rarely absent or greatly re- 

 duced. Wings lying parallel over the abdomen when at rest; basal 

 cells long; two or three submarginal cells, five posterior cells (four in 

 a very few genera) ; first and fourth posterior cells and the anal cell 

 either open or closed. 



The members of this family have usually been termed "Robber 

 Flies'' but I adopt ''Assassin Flies" as much more suitable as a com- 

 mon name. All the Asilidse are predaceous in the adult and probably 

 in the larval stages. The adults are found everywhere but many 

 groups of genera are restricted in habitat. Some will be found in 

 clearings in and around tbe edges of woods, some on sand near water, 

 others in open fields or on fallen trees or fenceposts. Some of the species 

 are found almost entirely on tree trunks w'hile others sit on the tips 

 of dead branches of trees or the tops of dead weeds. The species of 

 Leptogaster prefer long grass, particularly in moist places. Sandy 

 beaches will usually yield a few species. The species of Laphria and 

 Bomhonmna will usually be found resting upon leaves in the sun in 

 or at the edges of woods while the genera related to Asihia mostly 

 frequent open fields. 



