172 



BOYS AND GIRLS IN BIOLOGY. 



would come out in a few days. You can always find 

 plenty of babies, or pupje, and you can gather them and 

 watch them for yourselves. Sometimes, when you are 

 watching for the butterfly to burst through his silken 

 shell, you may see, instead, a whole swarm of black, 

 impish-looking flies. They are called the ichneumon- 

 flies, and their chief diet is caterpillar-flesh. Every 

 year they destroy thousands, and this is the way they 

 do it : the mother-fly (ichneumon) makes nests by 

 sticking little holes all along the back of the caterpillar, 

 and this only causes the caterpillar to squirm a little. 

 In these nests she lays her eggs, which hatch into little 

 white grubs, or worms. They feed on all the fat of the 

 caterpillar, but take good care not to touch any of his 

 organs, because, if the caterpillar dies, they would have 

 to die too. But, as soon as the caterpillar stops eating 

 and goes to sleep in his hammock, and so cannot pro- 

 vide any more food for the grubs, they fall to and 

 devour every morsel of him. When they have finished 

 their last meal, they take a nap themselves, and, while 

 they are sleeping, their outer-coat gets hard and bursts ; 

 and, just about the time that the poor caterpillar would 

 turn into the butterfly, out come the troop of black 

 flies. 



Now for the caterpillar's transformation. The pupa 

 or chrysalis skin turns dark, gets dry and brittle, and 



