17 



the caterpillars are carried by vehicles upon which they crawl or tirop^ 

 or upon the clothes of passers-by, and in this way many trees upon 

 which there were no egg masses become infested. 



The larval state lasts, on an average, from a month to five weeks. 

 When full grown, the larvse spin delicate grayish cocoons of silk mixed 

 plentifully with hairs. The mixture of hair is brought about by the 

 fact that the hairs are barbed and rather loosley attached to the body. 

 When a caterpillar begins to spin its cocoon the hairs of its body and 

 those of the long, black tufts on the prothorax first become entangled 

 with the silken threads and are pulled out. By the time the cocoon 



Fig. 6. — Tussock-moth caterpillar. Third and fourth stages, showing enlarged hairs from different 



parts of body (original). 



has begun to take shape, the characteristic long, black tufts of hair 

 have entirely disappeared from the body of the caterpillar. Later the 

 shorter hairs of the sides of the body become entangled and removed, 

 and finally many of the hairs composing the brush-like tufts upon the 

 fore part of the body are pulled out, and just before it transforms to 

 pupa the caterpillar bears but a remote resemblance to the individual 

 before it began to spin. 



The barbed hairs just mentioned may occasionally produce consid- 

 erable irritation of the skin of people upon whom the caterpillars may 

 have crawled or dropped from the trees. The hairs from the different 



