126 FIRST BOOK OF FORESTRY 



the eggs hatch much earlier, and instead of having only 

 one whole generation of the insects in a year, as in the 

 North, there are as many as three, so that the number of 

 insects increases very rapidly. 



With most of the moths that are dangerous to our for- 

 ests, both male and female are winged and fly. All of 

 them pass through the four distinct stages : egg, cater- 

 pillar, pupa, and adult or moth ; and all are injurious only 

 in the caterpillar state. 



Though some moths may be found in our woods every 

 season, it is only at long intervals that they become real 

 pests and cause great damage ; and even then the calamity 

 rarely lasts many years in succession. 



Since the caterpillars live on green leaves and buds, 

 trees of all sizes and ages are liable to their attack. Some 

 kinds of caterpillars prefer hardwoods, some conifers; 

 some eat all kinds, while a few of them eat leaves of only 

 one or a few kinds of trees. 



Where the caterpillars attack a pure stand of spruce 

 or pine forest, so that every tree furnishes the most 

 desirable kind of food, the trouble is naturally much 

 greater than in a mixed stand, where possibly half of 

 all the trees are entirely safe from the attack of this 

 particular insect. 



To prevent the ravages of caterpillars, the forester can 

 do but little. Where the land and climate permit, it is 

 well to raise only mixed woods. Generally it is well to 



