116 mPTEKA. 



tar is so offensive to insects that they cannot endure 

 soil impregnated with its odour. 



Bot-Fly (^Estrus bo vis) niagnified. 



The family of ^^stridcv contains those insects which, in 

 their larval stat^, are well known under the name of Bots^ 

 Wurmals, etc. These insects (^. bovis) deposit their 

 e^^gs on cattle, in whose bodies the larvae are nourished. 

 The presence of the fly is soon felt amongst the herd of 

 cattle ; with tails turned upon their backs or stretched 

 stifflv out in the direction of the spine, off they gallop 

 about their pastures in the wildest state of terror. An 

 allied fly {Mstrus ovis) (Fig. 13), infests sheep, laying 

 its eggs within the nostrils, from whence the maggots 

 make their way into the head, feeding on the mucilage 

 produced in the maxillary and frontal sinuses. When 

 ready to assume the pupa stage they fall to the ground 



