GENERAL LIFE HISTORY 55 



of the robber-flies, A. crabroniformis, is a conspicuously 

 fine insect. It equals the hornet in length, but is 

 more slender in body, tapering throughout the abdo- 

 men towards the tail ; it resembles the queen hornet 

 in colour. The dragon-flies also eat flies, but they 

 mostly feed upon winged aphides, gnats, and the like 

 small game. 



More secret destroyers of the fly brood are a few 

 rather obscure creatures akin in their nature to the 

 ichneumon flies, which are parasitic mainly but not 

 exclusively on lepidoptercc. Likewise, certain insec- 

 tivorous beetles share in the good work of fly 

 destruction. 



Flies are often observable encumbered with minute 

 vermin ; some of these are true lice, and some are 

 allied parasites called false-scorpions or chelifers. 

 These are acquired whilst frequenting dung and refuse 

 heaps, where they abound ; thus, probably cheese- 

 mites and the like are conveyed by flies into our 

 larders and warehouses. 



It is not only the web-weaving spiders which prey 

 upon the proverbially "silly" flies; there are also 

 roving spiders which do not contrive webs, and some 

 of these are nocturnal feeders ; the latter can only be 

 seen in daylight by looking for them underneath stones 

 and in other hiding places. 



Other fly destroyers are internal parasites, and these 

 include thread worms (Nematoidea), as well as Proto- 

 zoa of obscure kinds. These are being scientifically 

 studied by experts, and their life-history is as curious 

 as that of others of the same order, in that they pass 

 from one host to another, which fact for long helped 



