n 



ical change in its sap "appear to be necessary 

 for the well-being of the deposited eggs or the 

 youngsters that emerge from them. When these 

 beetles are numerous they freely attack and 

 easily kill the most vigorous of trees. 



The pine beetle is one of a dozen species of 

 bark beetles that are grouped under a name that 

 means "killer of trees." Each year they kill 

 many acres of forest, and almost every year 

 some one depredation extends over several thou- 

 sand acres. The way of each species is similar 

 to that of the others. The beetles of each species 

 vary in length from a tenth to a fifth of an 

 inch. They migrate in midsummer, at the time 

 of the principal attack. Swarming over the tree, 

 they at once bore into and through the bark. 

 Here short transverse or vertical galleries are 

 run, and in these the eggs are laid. 



In a short time the eggs hatch into grubs, and 

 these at once start to feed upon the inner bark 

 at right angles to the galleries, extending to 

 right and left around the tree. It does not re- 

 quire many of them to girdle the tree. Com- 

 monly the tree is dead in two months or less. 



177 



