12 THE IMPORTANCE OF BIRD LIFE 



dred thousand .species already recognized, and 

 virtually all ,are capable of multiplying at an ap- 

 palling rate. 



With this great potentiality for reproduction, 

 then, insects cannot be allowed to go unchecked; 

 otherwise within a short time, the surface of the 

 earth would be a wasted desert. Fortunately 

 nature has provided a multitude of enemies, 

 more, indeed, than birds ever dreamed of having. 

 Thus, the mycelium of certain fungi (the thread- 

 like body of the plants) thrives on the bodies of 

 certain insects; diseases blight them; frost and 

 flood cut short their lives; animals, like the ant- 

 e.ater, make of them a sole source of food; para- 

 sites flourish and grow fat upon them ; they wage 

 continual war among themselves; and birds de- 

 stroy them parasites, predaceous forms, and all. 



But while this form of destruction is perhaps 

 the greatest mission of birds in nature, it also is 

 of the highest economic importance to agri- 

 culture and will be discussed more at length in 

 the next chapter. 



4 

 Effect on Vegetation 



The next great avian function falls under two 

 apparently opposite heads: the limiting of vege- 

 tation and the spreading of vegetation. 



