DIPTERA 



CHAP. 



Fam. 17. Therevidae. 



the appearance of short 



Moderate-sized flies, with somewhat 

 Asilidae. Tliei/ linre, hoirerer, only a 



feeble //<*//// proboscis, and minute claws, with pulinlli hut no' 



e in /indium ; the antennae project, are short, 

 three -jointed, pointed. The flies of this 

 family care believed to he predaceous like 

 the Eobber-flies, but they appear to be very 

 feebly organised for such a life. We have 

 about ten species in Britain, and there 

 are only some 200 known from all the 

 world. But little is known as to the meta- 

 morphoses. Meigeii found larvae of T. 

 nohilitdta in rotten stumps, but other larvae 



FIG. 231,Therera (Psilo- 



cephala) confinis. A, have been recorded as devouring dead pupae 

 Pupa ; B, larva Euro!*. or i arvae o f Lepidoptera. The larvae are said 



(Alter Perns.) 



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



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

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

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

 in the larval skin; that of Psilocephala is armed with setae and 

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



Fam. 18. Scenopinidae. luitlier x>n<dl ///<*, witlnmt bristle*. 

 Antennae three-jointed, the third joint rather Ion;/, without j>- 

 pendage. ProJioscis not jirojecting. Empodium ahsent. These 

 unattractive Mies form one of the smallest families, and are 

 chiefly found on windows. >S'. fenextndis looks like a tiny 

 Si ratiomyid, with a peculiar, dull, metallic surface. The larva 

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

 strange substances, but Osten Sacken is of opinion ! that it is 

 really predaceous, and frequents these substances in order to find 

 the larvae that are developing in them. If so, Scenopinus 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 head placed like a hook at one extremity of the body 

 and with two short, divergent processes at the other extremity, 

 almost exactly like the larva of There m. Full references to the 

 literature about this Insect are <riven bv Osten Sacken. 



O i/ 



Fam. 19. Nemestrinidae. These Insects appear to be allied 

 to the Bombyliidae. They are of medium size, often pilose, and 



1 Eut. Muy. xxiii. 188(3, p. 51. 



