332 THE GYPSY MOTH. 



small silk mat, a little longer in diameter than the length of 

 the body of the caterpillar. When rocks have been burned 

 over, caterpillars have been seen spinning down to escape the 

 smoke and heat. They frequently spin threads from fences 

 to the neighboring trees. The insect also spins a scanty 

 cocoon for a shelter and support during the pupal stage. 



The Process of Pupation. 



Cocoon. When the caterpillar is fully grown, it seeks 

 some sheltered spot (Plates 47, 49), and rests quietly for 

 about twenty-four hours. It then empties its alimentary 

 canal, the discharge being of a semi-fluid nature, and con- 

 taining an abundance of chlorophyl, showing it to be, in 

 part at least, the remains of food. In about one hour after 

 this discharge, the caterpillar begins to spin a frail cocoon, 

 which is composed of a few coarse brown silken threads, 

 occasionally enclosing a leaf or other material. In spinning, 

 it first places its spinneret close to the surface on which the 

 cocoon is to be formed, and presses out a drop of the silk- 

 forming fluid, which serves as an anchor for the silk thread 

 which is then spun out. It first spins a few long threads, 

 which usually exceed the length of the cocoon when finished. 

 After a number of these long threads, which connect various 

 points and serve as a sort of frame, have been formed, the 

 caterpillar begins to spin more rapidly, and to place short 

 threads between the long ones, working always from the 

 inside, and changing at intervals from one side of the cocoon 

 to the other. Where the threads cross each other they are 

 fastened together by a drop of the fluid in much the same 

 manner as at the starting of the cocoon. In spinning, the 

 labial palpi and the feet are used to grasp the threads. As 

 a rule, the spinning is not completed at a single operation, 

 since the caterpillar rests several tunes, the rests ranging 

 from a few minutes to five or six hours. The actual time 

 spent in spinning is about six hours. After completing its 

 network of silk the caterpillar rests quietly, except for occa- 

 sional spasmodic twitchings of the body, hanging head down- 

 ward, and pupates at the end of about three hours. 



Pupation. When the process of pupation begins, the 

 skin commences to contract and wrinkle on the posterior 



