THE BOT-FLY OF THE HORSE 



I4S 



Fig. 8i. — Bot-fly of horse, male. 

 After Bracy Clark. 



he know how much trouble will arise from these apparently 

 insignificant attentions ! 



A female fly, bent upon laying her eggs, hovers about the 

 horse with her body almost vertical, 

 and now and then, hardly settling, 

 touches his skin with the tip of her 

 abdomen. At that instant a sticky 

 egg is passed out and glued to one 

 of the hairs, usually near its tip. 

 In a very short time the sticky 

 substance sets hard, and the egg 

 is then so firmly cemented that 

 no ordinary means can remove it. 

 The eggs are not laid at random, 

 but most commonly upon the inside 



of the knee, on the flanks, or on the hinder part of the 

 shoulder, never on any part of the horse which is out of 

 reach of his tongue. When the first egg has been made 

 fast, the fly retreats for a moment, brings a second egg into 

 the tube, and returns to attach it in the same way. One 

 female fly may contain 600-700 eggs, and nearly that number 

 will sometimes be found on a single horse. The eggs are 

 white when quite fresh, afterwards turning yellow, and since 



they are large enough to be seen 

 by the naked eye, they are some- 

 times very conspicuous on a dark- 

 coloured animal. The fly delights 

 in warm, sunny weather, and shelters 

 during cold or rain, so that we can 

 guess when eggs are likely to be 

 laid ; it does not .enter stables. 



The eggs of the bot-fly are 

 destined, if fortune favours them, 

 to produce larvK, which will enter 

 the stomach of the horse, and 

 there feed at his expense till they 

 are ready to pupate. We might guess that the horse would be 

 induced in some way or other to swallow the egg, and so at once 

 make himself the dupe of the fly. But this is not precisely the 

 method of nature. The egg is cemented so fast that the horse 

 cannot remove it. On reflection, we see that the purpose in 



Fig. 82. — Bot-fly of horse, female. 

 After Bracy Clark. 



