412 



ANIMAL BIOLOGY 



loss attributed to this army of silent tree-killers is staggering. 

 They destroy two-thirds as much of the nation's wealth each year 

 as do forest fires — timber equal to one-fifth of the wood produced 

 annually in the United States. At the present time these destruc- 

 tive insects recognize neither limits nor boundaries, for their march 

 has received relatively little resistance. And resistance is not easy 

 when we recall that some insects may travel hundreds of miles on 

 the wings of the wind — aviators have trapped them more than 

 two miles aloft. 



The Mountain Pine Bark Beetle, after invading the forests 

 of the Northwest, now is threatening those of the Yellowstone 



Fig. 262. — Gypsy Moth, Porlhetria dispar. A, larva; B, pupa; C, adult 



female. (From Howard.) 



National Park. The Gypsy Moth, accidentally introduced near 

 Boston, has spread throughout a large part of southern New 

 England and is besieging the New York State line. Entomologists 

 have made intensive studies of its European enemies, left behind 

 when it came to America, and the introduction of some of these 



