194 



SCHOOL ENTOMOLOGY 



them through shrubbery or water to escape. As the fly 

 causes no pain it is evident that this fright is instinctive. 

 When the animal licks the parts on which the eggs are laid, 

 the eggs hatch and the young larvae are taken to the mouth, 

 as in the case of the horse bot. They then penetrate the 

 walls of the oesophagus and migrate through the connective 

 tissues of the body for several months, working their way to 



beneath the skin on the neck 

 and then backward until they 

 become lodged beneath the 

 skin in the region of the 

 back. The larva now makes 

 a hole through the skin so as 

 to secure air for breathing. 

 It develops rapidly, subsist- 

 ing on pus and serum which 

 its presence induces, and 

 causes a characteristic swell- 

 ing or tumor. When full 

 grown it is an inch or more 

 long so that it may cause 

 considerable irritation. It 

 then works its way out 

 through the hole which it 

 had made, drops to the ground, which it may enter, or it 

 may change to the pupa on the surface. The final trans- 

 formation to the adult fly takes place from three to six 

 weeks later, there being but one generation a year. 



Various oils and repellent substances have been recom- 

 mended for smearing on cattle to prevent the attacks of 

 the flies, but it seems that there is no very conclusive evi- 

 dence of their efficacy, and it is certain that the applications 

 must be made every few days, so that such treatment is 



FIG. 137. Ox warble (Hypoderma 

 lineata), female, natural size 

 indicated by side line. (From 

 "Insect Life.") 



