5° 



Insects and Disease 



BOT-FLIES 



Another group of flies known as the bot-flies 

 (Fig. 30) have their mouth-parts rudimentary or 

 entirely wanting so of course they themselves can- 

 not bite or pierce an animal. Nevertheless they 

 are the source of an endless amount of trouble to 

 stockmen and sometimes even attack man. Al- 

 though these flies cannot bite, the presence of even 

 a single individual may be enough to annoy a horse 

 almost to the end of endurance. Horses seem to 

 have an instinctive fear of them and will do all in 

 their power to get rid of the annoying pests. 



The eggs of the house bot-fly are laid on the 

 hair of the legs or some other part of the body. 

 The horse licks them off and they hatch and 

 develop in the alimentary canal of their host. 

 Sometimes the walls of the stomach may be 

 almost covered with them thus of course seriously 

 interfering with the functions of this organ. When 

 full grown the larvae pass from the host and com- 

 plete their transformation in the ground. 



The bot-flies of cattle or the oxwarbles (Fig. 31) 

 gain an entrance into the alimentary canal in the 

 same way, that is, by the eggs being licked from the 

 hairs on the body where they have been laid by 

 the adult fly. But instead of passing on into the 



