14 CATERPILLARS AND THEIR MOTHS 



caterpillars always eat the cast skin, with, the excep- 

 tion of the mask. 



At molting-times caterpillars are delicate and should 

 not be disturbed or touched if this can be avoided. 

 The early molts, especially, seem to be critical periods, 

 and more caterpillars die then than at any other time 

 in the history of a brood indoors. Of course out of 

 doors many are killed by birds, squirrels, mice, toads, 

 snakes, and so forth, and stung by parasitic flies. 



After the last molt the caterpillar increases in size 

 more rapidly than before, and eats voraciously. When 

 full grown and ready to pupate, it stops eating, stays 

 quiet for a day or so, and then begins crawling about 

 as if in great haste to find a suitable place in which to 

 spin or burrow. Usually its colors change somewhat, 

 some larvae growing pink on the back, others lead- 

 colored, while others merely grow duller and the marks 

 look faded out. The caterpillar empties its intestine, 

 generally before it begins the rapid crawling, and in 

 some cases the almost fluid discharge is one of the 

 first indications of approaching pupation. 



Very few caterpillars have just the same marks and 

 colors when they come from the egg and when they 

 are ready to pupate. Most of them pass through one 

 or more changes of appearance in the course of their 

 molts, and usually are more elaborately marked in the 

 later stages. The changes of appearance through 

 which the individual caterpillar passes between egg 

 and pupa are thought to show the forms through 

 which the species has passed in the course of its evolu- 

 tion from the original form. 



The skin of a caterpillar may be smooth, rough or 



