484 



DIPTERA 



CHAP 



-Tliereva {PsUo- 

 cephala) confinis. A, 

 Pupa; B, larva. Europe. 

 ( A.lter Perris. ) 



Fam. 17. Therevidae. — Moderate-stzed flics, with somewha, 

 the ap2)carance of short Asilidae. They hare, however, only e 

 feeble fleshy jJi'oboscis, and minute claws, tvith indrilli, hut m 

 eynpodium ; the antennae project, are short 

 three -jointed, piointed. — The flies of this 

 family are believed to Ije predaceous like 

 the Eobber-flies, but they appear to be verj 

 feebly organised for such a life. We havt 

 about ten species in Britain, and there 

 are only some 200 known from all tht 

 world. But little is known as to the meta- 

 morphoses. Meigen found larvae of T 

 nvhilitata in rotten stumps, but other larvae 

 have been recorded as devouring dead pupae 

 or larvae of Lepidoptera. The larvae are saic 

 to be elongate, very slender, worm-like, anc 

 to have nineteen body-segments, the posterior pair of spiraclet 

 being placed on what looks like the seventeenth segment, but h 

 really the eighth of the abdomen. The pupa is not enclosed 

 in the larval skin ; that of Fsilocephcda is armed with setae anc 

 spinous processes, and was found in rotten wood by Frauenfeld. 



Fam. 18. Scenopinidae. — Rather small flies, without bristles 

 Antennae three-jointed, the third joint rather long, vnthout ap- 

 piendage. Proboscis not jJi'OJecti^ig. Enipjodium absent. These 

 unattracti^'e flies form one of the smallest families, and are 

 chiefly found on windows. S. fenestralis looks like a tinj 

 Stratiomyid, with a peculiar, dull, metallic surface. The larvs 

 of this species has been recorded as feeding on a variety o\ 

 strange substances, but Osten Sacken is of opinion^ that it if 

 really predaceous, and frequents these substances in order to fine 

 the larvae that are developing in them. If so, Scenojnnus is useful 

 in a small way by destroying " moth," etc. The larva is a little 

 slender, cylindrical, hard, pale worm of nineteen segments, with a 

 small brown liead placed like a hook at one extremity of the bodj 

 and with two short, divergent processes at the other extremity 

 almost exactly like the larva of Thereva. Full references to the 

 literature about this Insect are given by Osten Sacken. 



Fam. 19. Nemestrinidae. — These Insects appear to be alliec 

 to the Bombyliidae. They are of medium, size, often piilose, anc 



1 Ent. Mug. xxiii. 1886, p. 51. 



