LIFE HISTORY OF A BUTTERFLY 



29 



eggs on the milkweed, for the young feed upon no other plant. The 

 eggs hatch out in four or five days into rapidly growing wormlike 

 caterpillars, each of 

 which will shed its 

 skin several times be- 

 fore it is full grown. 

 These caterpillars pos- 

 sess, in addition to the 

 three pairs of true 

 legs, additional pairs 

 of prolegs or cater- 

 pillar legs. The ani- 

 mal at this stage is 

 known as a larva. 



Formation of Pupa. 

 After a life of a few 

 weeks at most, the 

 caterpillar stops eat- 

 ing and begins to spin 

 a tiny mat of silk upon 

 a leaf or stem. It at- 

 taches itself to this 

 web by the last pair 

 of prolegs, sheds its 

 skin again, and hangs 

 there in the dormant stage known as the chrys^alis or pupa. 

 This is a resting stage during which the body changes from a 



caterpillar to a butterfly. 



The Adult. After a week or more of 

 inactivity in the pupa state, the outer 

 skin is split along the back, and the 

 adult butterfly emerges. At first the 

 wings are soft and much smaller than in 

 the adult. Within fifteen minutes to 

 half an hour after the butterfly emerges, however, the wings are 

 full-sized, having been pumped full of blood and air, and the insect, 

 after her marriage flight, is ready to follow her instinct to deposit, 

 her eggs on a milkweed plant. 



Monarch butterfly : adults, larvae, and pupa on their 

 food plant, the milkweed. (From a photograph 

 loaned by the American Museum of Natural History.) 



Spiracle 



Head 



True fegs 

 Caterpillar of 



Prolep 



moth, the 

 squash borer. 



