16 



ELEMENTARY STUDIES IN INSECT LIFE 



For a long time the larva rests quietly, and the skin 

 becomes like an old garment. Undulatory movements 

 of the body headward, slow at first, then increasing, 

 crack the skin around the neck; the caterpillar, pulling 

 itself forward, pushing the skin backward, throbs and 

 pulsates until the skin crumples up unbroken at the 

 end of the body. The head is thrashed about from side 

 to side, occasionally rubbing and striking the stalk, 

 until the hood is discarded. From ten to fifteen min- 

 utes of its lifetime arc required for each change in 



FIG. 17. Caterpillars of black swallowtail about to molt. 

 Photographed from life. 



clothing. The caterpillar, with its new, whitish, almost 

 colorless coat, rears up its head, remains nearly motion- 

 less for about an hour. This is time sufficient for the 

 characteristic colors to develop and for recuperation. 

 Prompted by the same instinct which caused it to con- 

 ceal its shell-house, its first act now is to turn around 

 and devour the old covering. The fasting, the exertion 

 in eating the skin, every act of the whole performance 

 tends to sharpen the appetite. It eats voraciously, not 

 the tender flowers as before, but the seed-pods and large 



