106 USEFUL BIRDS. 
that during the first few years after its introduction into a 
locality its inroads on the foliage were not noticeable ; nearly 
all the insects resulting from each egg 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 much 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 
through 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 many 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 
