^02 



TENTH ANNUAL REPORT. 



were washed away or destroyed. As a rule only those survived 

 which were able to shelter themselves on the under surface 

 of the twig to which the egg mass was attached. Conse- 



Fig. 9. — American Tent Caterpillars killed 1)y disease. 



quently, at the beginning of the season there was a consider- 

 able reduction in the numbers of the caterpillars. The sur- 

 vivors, however, developed in sufficient abundance to be de- 

 cidedly in evidence in May, but during the last weeks of their 

 grovrth there appeared among them a bacterial disease, a sort 

 of insect cholera, which killed them in vast numbers. The 

 effectiveness of this disease was doubtless increased by the "wet 

 weather prevailing at the time. Early in June nearly every 

 nest was full of the dead and dying caterpillars, those upon 

 the outside of the web hanging limp and lifeless at first (Fig. 

 9), and then gradually shriveling up until only the dried 

 skins told of their presence. A series of observations made 

 upon a large number of nests just before the period of pupa- 



