SHALL WE PAY OUR DEBT? 359 



live and breathe among them in their unchecked 

 development. Smaher in size but tireless on wing 

 and taking larger prey, I should class with the air 

 police the gnatcatchers and fly-catchers. 



Invaluable around any premises I count the 

 work of the common house wren, which will raise 

 three broods, averaging from six to eight young to 

 the nest. This keeps wrens food-hunting from 

 dawn until dark, taking everj^ insect they see from 

 a mosquito to a spider. The largest insect I ever 

 pictured a wren carrying into his house was a 

 dragonfly stripped of its wings. 



It is one of the mysterious, inscrutable workings 

 of evolution that our real safety depends upon the 

 warbler family, its members so tiny that they are 

 not much bigger than wrens, most of them of pro- 

 tective colour of green and gold like the leaves of 

 the trees, of steel and slate grey and white like the 

 bark of tree trunks, painted, sj^lashed, and mottled 

 colours like the flowers, blue like the sky, or dark 

 blue like the shadowed waters, the gayest, gaudiest, 

 little feathered throng on earth, the almost invisible 

 host that hunts among the leaves. They have 

 featherlight bodies, indistinguishable among the 

 leaves, bright eyes, tiny, pointed beaks, with which 

 they search under and over the foliage of vines, 

 bushes, orchards, and giant forest trees, hunting 

 out millions and billions of insect eggs, larvae, 

 aphis, plant lice, and tiny, newly hatched cater- 

 pillars that, if allowed to mature, would develop 



