128 



THE SPINY ELM CATERPILLAR 



the caterpillars. At the end of the week they moult or cast 

 their skins, a process in which the skin of each insect splits 

 open along the back, and the caterpillar crawls out of it, 

 being covered with a new skin that had been formed beneath 

 the old one. This new skin stretches somewhat after the 

 caterpillar emerges, so that the insect is able to increase con- 



Fig. 44. Colony ot CaterpiUars feeding upon wiHow. 



siderably in size. At the period of moulting the caterpillars 

 remain quiet for a short time, but they soon become active 

 again and begin feeding with increased voracity. 



During the next three weeks this moulting process is re- 

 peated three times, the caterpillars becoming larger each time, 

 and leaving their cast skins upon the denuded twigs, as shown 

 in Fig. 43. They soon scatter more or less over neighboring 



