PROC. ENT. SOC. WASH., VOL. 22, NO. I, JAN., IQ2O 13 



Plate 2. 



Fig. 1. Deretaphrus oregonensis ventral view of thorax and head. 



Fig. 2. Deretaphrus oregonensis dorsal view of pupa. 



Fig. 3. Deretaphrus oregonensis ventral view of head. 



Fig. 4. Aulonium tuberculatum dorsal view of thorax of pupa. 



Fig. 5. Ditoma crenata dorsal view of pupa. 



Fig. 6. Bothrideres geminatus leg. 



Fig. 7. Nematidium filiforme -dorsal view of thorax of pupa. 



Fig. 8. Ditoma crenata -dorsal view of ninth abdominal segment. 



Fig. 9. Bothrideres geminatus labrum and maxillae. 



Fig. 10. Bothrideres geminatus right mandible from side. 



Fig. 11. Bothrideres geminatus -right antennae. 



Fig. 12. Deretaphrus oregonensis left mandible from below. 



Fig. 13. Deretaphrus oregonensis spiracle. 



Fig. 14. Nematidium filiforme lateral view of eighth and ninth abdominal 



segments. 



Fig. 15. Deretaphrus oregonensis lateral view of body. 



ABBREVIATIONS. 



C, cardo; gu, gula; ha, arm of hypostoma connecting with hypopharynx 

 (hypopharyngeal bracon) ; 1, ligula; Is, labial stipes; m, mentum; pf, palpi- 

 fer; ps, presternum; r, retinaculum; s, stipes of maxillae; sj, supplementary 

 joint of antennae; ta, tentorial arms. 



DISTRICT OF COLUMBIA DIPTERA: ASIL1DAE * 



BY W. L. McATEE AND NATHAN BANKS. 



The family Asilidae comprises flies which vary in size from 

 small to extremely large. A much-used English name for the 

 group is robber-flies, a most inappropriate term, for which assas- 

 sin-flies would be a good substitute. The species are uniformly 

 predacious, have a characteristic leggy, grasping appearance and 

 voracious appetites. They prey upon other insects, taking toll 

 from nearly all groups. vSome of the larger species are as watchful 

 as hawks, swift in action and correspondingly difficult to cap- 

 ture. Sunny paths and roads are a favorite resort for many of 

 the species; some sit on bare trunks and poles, some on leaves, 

 the tips of dead twigs or blades of grass, and a few in the shade. 

 The different genera and species have quite characteristic habits 

 in this respect, making search for them a source of constant 

 interest to the collector. 



1 For tin- Syrphidae, see Proc. Biol. Soe. Wash., L".), pp. 17:; 120-4, Sept. 12 12, 

 ini(>; and the Tabanidae, 1'roe. Knt. Soc. Wash., Vol. 120, pp. 188-206. Dec. 

 1918. 



