128 FIKST BOOK OF FORESTRY 



keep the woods well cleaned and thinned ; and in all cases 

 we should encourage and protect all kinds of insect-eating 

 birds and also such animals as the shrew, mole, and bat. 



In Europe large sums have been expended in collecting 

 egg masses as they cling to the bark of trees, also in col- 

 lecting the pupae and killing the young caterpillars while 

 they are still in large clusters together. 



. These methods have also been tried in our country, 

 but only for the protection of shade trees. In Bavaria 

 and other states all the trees of entire forests have been 

 supplied with rings of a special sticky preparation, which 

 keeps the newly hatched caterpillars from climbing the 

 stem and causes them to perish in large numbers. 

 Though this has been successful in some cases, it is 

 generally too expensive, 



When once the caterpillars exist in large numbers 

 man's efforts are entirely in vain; for while it is quite 

 easy to spray a few peach trees when infested, the use of 

 a poison spray in the woods is out of the question; the 

 trees are too large and the cost too great. 



Fortunately, the multiplication of the injurious insects, 

 whether bark beetles or caterpillars, causes a multiplica- 

 tion of their strongest enemies, predaceous and para- 

 sitic insects, and disease. 



A large number of widely differing kinds of insects are 

 hunters and live exclusively on other insects, eating or 

 destroying them in every state, preferably.as larvae (grubs, 



