52 CATERPILLARS AND THEIR MOTHS 



usually kill some ; aud a margin should be allowed 

 for such losses, for one may not have a brood of the 

 same kind again for years. There is as much luck in 

 moth-hunting as in fishing, and one can never be sure 

 of the " catch" until it is at home, so it is well to make 

 the most of a present chance. 



Even when found, caterpillars are not always 

 "good." They may be stung by parasitic flies, and 

 though they may live through pupation, the fly-larvae 

 will devour their tissues and so destroy them, and only 

 flies will emerge. Sometimes we find caterpillars with 

 the white eggs of the fly on their heads or bodies. If there 

 are not too many eggs, and if they are so fresh that 

 the grubs have not left them and eaten their way into 

 the caterpillar's body, we remove them with either a 

 knife or small forceps, and the caterpillar is safe. If 

 the eggs give a yellow liquid when crushed by the 

 forceps, they have not hatched. The caterpillar will 

 squirm while under treatment, and care must be taken 

 not to squeeze it too much or to injure its skin with 

 the knife. Some flies pierce the skin and lay their 

 eggs inside the body of the caterpillar, and in this case 

 we cannot save it or even know that it is stung. 



Moreover, all one's pupae may not live to give the 

 moth. Sometimes a fungus covers them and kills 

 them. Sometimes they dry up from some unknown 

 cause, others in the same box being perfectly healthy. 

 Sometimes they liquefy and decay without any appa- 

 rent reason. Taking all these possibilities into con- 

 cideration, one can hardly have too many pupae or 

 cocoons of any kind. 



It is much work to care for a large supply of cater- 



