No. 4.] BIRDS AND CATERPILLARS. 337 



7. Birds as a class must be considered as a potent factor 

 in regulating the increase of those moths whose caterpillars 

 are covered with hairs or spines. Many outbreaks of such 

 species are "nipped in the bud" by birds, and they have a 

 large share in the repression of the greater outbreaks. 



8. As certain hairy caterpillars are among the worst pests 

 known to the farmers and fruit growers, those birds which 

 destroy such caterpillars, and which are also in other ways 

 to be considered among our most useful species, should be 

 protected, even if some of them take small wages of fruit 

 to pay for their services. 



