8 THE HUMAN SIDE OF TREES 



that a sudden invasion of exceptionally large hordes 

 of some particular species has often depopulated 

 entire tree cities at different times in the world's 

 history. In recent years the people of South Da- 

 kota and Wyoming have, seen vast areas ruined 

 by the depredations of bark-beetles; and only the 

 combined efforts of the United States Department 

 of Agriculture and the authorities of several of the 

 New England States prevented very serious re- 

 sults as an outcome of the invasion of the gipsy 

 moth and the browntail moth. Insects can be held 

 accountable for most of the forest fires. A wide- 

 spread raid fills many square miles with the bodies 

 of their victims, and there is admirable tinder for 

 the lightning to set ablaze. 



In combating vegetable and insect enemies, the 

 trees often make defensive alliances with other 

 more friendly neighbours. They shelter birds, 

 moths, ants, squirrels, and other creatures, and even 

 feed them with their fruit, in order to be provided 

 with aerial squadrons and standing armies to fight 

 for them. It is to the dependents' interest to pro- 

 tect their benefactor against all comers. Right 

 loyal is their service. 



A weak or invalid tree we have many times seen ; 

 but we do not ordinarily think of trees as being 

 subject to disease in the way human beings are. 



