CHAPTER IV 

 MYIASIS AND THE (ESTRID& 



The family of the GLstrida is the most curious and 

 horrific of all the different tribes of flies ; it is very 

 limited in species, of which five or six are prevalent 

 throughout Great Britain. The worst of these could 

 be almost exterminated with ease, but unfortunately 

 mistaken ideas have prevailed, and graziers commonly 

 believe that though the sheep's nostril fly is con- 

 spicuously harmful and dangerous, the horse's bot-fly 

 and its congeners are negligible as regards the 

 practical health of the host. The bot-fly and the 

 worble-flies are all of a largish size, only the sheep's 

 nostril fly and CEstrus hcemorrhoidalis, which latter 

 infests the throat and rectum of the horse, are of a 

 medium size. 



It has been known from very ancient times that 

 man himself was not exempt from some fly, which was 

 imagined to resemble the horse's bot-fly, and it has 

 been wrongly surmised that many different creatures 

 and all ruminant animals were more or less subject to 

 the attacks, each one of its own kind, of cestrid fly. It 

 is undeniable that man is sometimes internally afflicted 

 with dipterid larvae, but it is most certain that the fly 

 to be incriminated is not a congener of the horse's 

 bot-fly. 



