106 USEFUL BIRDS. 



that during the first few years after its introduction into a 

 locahty its inroads on the foliage were not noticeable ; nearly 

 all the insects resulting from each Q^g cluster fell victims to 

 their natural enemies. This is true to a still greater extent 

 of most of our native insects. As the season advances the 

 few large caterpillars that are left from each brood injure the 

 leaves a little, so that on close inspection in July the foliage 

 appears somewhat ragged and riddled, but at a distance, or to 

 the casual observer, the trees seem in fine foliage. 



He who watches the birds feeding from day to day can 

 only wonder how they can possibly find so many caterpillars ; 

 for birds do find them continually, by going over the same 

 ground day after day. When it is difficult for us to see 

 even a single specimen on the leaves, the birds continue to 

 find them until summer wanes and the leaves begin to fall. 



The value of the service performed in woodlands by birds 

 that eat caterpillars is far greater than it seems at first sight, 

 for wherever the foliage of a tree is destroyed by insects the 

 fruit of that tree cannot mature, and the tree also suffers a 

 serious check in growth. There is nmch woodland in Massa- 

 chusetts that pays very little in excess of the taxes. A leaf- 

 less tree makes no wood growth ; therefore, whenever trees 

 that are grown for wood or lumber are stripped of their 

 leaves by caterpillars, the size of the annual wood ring is so 

 much below the normal that the owner realizes no profit, and 

 may even suffer a loss on his wood lot that year. 



But this is the least danger that is threatened by the attacks 

 of caterpillars. Most people know that the tree "breathes 

 throuijh its leaves," and when for a long period these organs 

 are prevented from developing, it must inevitably die. Most 

 coniferous trees, like the pine and hemlock, die when stripped 

 of their foliage for one season ; and deciduous or broad- 

 leaved trees, such as the oak, ash, and maple, often succumb 

 if deprived of their leaves for a considerable length of time 

 each year for even two or three years in succession. Most 

 trees would soon be killed in this way were it not for the 

 birds, for there is a succession of man}^ species of caterpillars 

 that feed upon the trees all summer, and, were they not held 

 in check by birds, they would destroy the foliage month 



