Parasites and Predators 



disaster awaits the whole brood. This happens in the 

 case of a little wasp, with the uncomfortable habit of 

 laying its eggs on the backs of caterpillars. Now a good 

 fat caterpillar may be described in very unscientific 

 language as a juicy individual ; when his thin skin is 

 punctured his vitals quickly dry up. 



The grubs of the wasp we mentioned come into the 

 world on the back of a caterpillar and they all begin to 

 feed at holes in the skin of their host. So long as they 

 keep their heads buried in his flesh, all well and good, but 

 should one of them meet with mishap or cease feeding, 

 a most unlikely event, his host will rapidly dry up, losing 

 his moisture from the open wound in his skin. The 

 result of this would be that all the other wasp grubs would 

 die from lack of nourishment. Now most caterpillars feed 

 for some time, and as they do so they grow and cast their 

 skins several times before they are fully fed. 



In the case of our wasp grub, Nature, as though fearing 

 that misfortune might overtake the grubs were they long- 

 lived, has ordained that they shall attain their full develop- 

 ment in three days. In fact the whole life cycle of this 

 little wasp, from mother insect to egg, from egg to grub, 

 from grub to chrysalis and again to prospective mother, is 

 completed in the remarkably short time of a week and 

 a day ! 



One of the most extraordinary of insect parasites is 

 known as the ant-decapitating fly. It is almost brutal in 

 its methods. The little fly deposits a single egg on the 

 neck of a common black American ant. When the grub 

 hatches from the egg it loses no time in boring into the 

 head of its living host. As it grows it gradually fills the 

 whole head cavity, till at length the unfortunate ant 

 gradually loses that useful member. The grub still hides 

 within the shell of a head, feeding on such morsels as the 

 brain, but the hinder parts of its body project from its 

 shelter, so that we are presented with the curious spectacle 

 of the ant's head, apparently, walking about on its own 



301 



