The Food of BinLs. 159 



of predaceous insects rest, will have the most hesitation in 

 trusting them without reserve. 



I would also call attention to the fact that we do not yet 

 know that the normal rate of increase among these carniv- 

 orous and parasitic insects is not sufficient to keep their 

 numbers full to the limit of their food supply, and to fur- 

 nish also a surplus for destruction by birds. Just as a tree 

 puts forth more leaves than it needs, and sets more fruit 

 than it can possibly mature, as an offset to the constant, 

 normal depredations of insects, so there is much reason to 

 suppose that our insect friends have become adjusted to 

 this steady drain on their numbers. 



