The Food of Birds. 
159 
vations upon which our general statements of the food 
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 
carnivorous and parasitic insects is not sufficient to keep 
their numbers full to the limit of their food supply, and 
to furnish 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 be- 
come adjusted to this steady drain on their numbers. 
