ABUNDANCE AND INJURIES 



137 



ABUNDANCE AND INJURIES 



As a rule the caterpillars of the Mourning Cloak Butter- 

 flies are to be found only in occasional colonies, so that the 

 damage they do attracts little if any attention. But some- 

 times the weather or other conditions are so favorable to their 



Fig. 50. Poplar twig denuded by caterpillars, showing carpet web. 



development that they multiply beyond this normal limit and 

 are to be found in great numbers. At such times serious 

 damage is often done. In this country such local outbreaks 

 of the species have frequently occurred, generally, however, 

 over very limited areas. So far as I can learn the insect has 



