32 THE IMPORTANCE OF BIRD LIFE 



Destruction of Insects by Birds 



In the instinctive efforts of birds to maintain 

 the balance of agriculture, they devour many use- 

 ful species of insects. Their instinct is to fill 

 their crops with food. A robin cannot be expected 

 to distinguish between economically desirable 

 beetles and bad ones. A "good" robber-fly and 

 a "bad" house-fly probably taste much alike to 

 a kingbird. A night-hawk would rather swallow 

 a tiny Microgaster than a June-bug. They con- 

 sume all species, beneficial and harmful alike. 



An examination, however, of numerous bird 

 stomachs has shown that the larger proportion 

 of insects taken is made up of vegetable-eaters. 

 This is not surprising when we stop to consider 

 that the vegetable-eaters far outnumber the other 

 forms in nature. Both are destroyed in propor- 

 tion to their numbers. 



It so happens that, as in the case of the 

 cabbage-caterpillar, the vegetable-eater is not 

 destroyed by parasites until great damage to 

 crops has been accomplished. The second gen- 

 eration, it is true, is reduced in numbers, but not 

 before the first generation has inflicted serious 

 loss upon the farmer. Birds, therefore, by 

 consuming the caterpillar, though with it a num- 

 ber of parasitical larvae may be destroyed, are 



