itASON AND LEFHOY. 369 



not exempt even in their pupal condition in the soil, the Hoopoe 

 especially probably getting many in this way'; even as moths they 

 are attacked, though in this stage their protective attitudes and 

 colouration protects them to some extent. So too for almost every 

 class of destructive insect : grasshoppers are extensively eaten and 

 have little protection, except when on swaying plants which afford 

 little foothold to birds ; even the larger locusts are attacked ; ter- 

 mites are enormously eaten in the stage in which they are capable 

 of forming new nests. Beetles are extensively eaten and so are> 

 to a less extent, the bugs. On the other hand there is little destruc- 

 tion of predaceous insects which are beneficial to agriculture ; the 

 enormous host of parasitic Ichneumons and Tachinid flies are not 

 eaten, Mantids, predaceous bugs, the predaceous Asilids are practi- 

 cally untouched ; the insects feeding on Aphides, the Ladybird 

 beetles and Chrysopids are untouched ; the digger wasps and true 

 wasps which constantly check insects are not fed on ; and there is 

 scarcely a beneficial insect which is checked to any extent by birds. 

 To anyone who has studied the influence of these beneficial insects, 

 this immunity they have is an enormous factor in preserving the 

 balance of life and in maintaining that equable balance of life which 

 never lets one species become destructively abundant but preserves 

 an equality of all; and that is, to man, the really important thing. 

 It is difficult to overestimate the value of birds as a class and their 

 special function seems to be, not so much the keeping down of indi- 

 vidual destructive species (which is done by the special parasites 

 each destructive insect has), as the cutting off of the crest of the 

 wave of increase, the checking of those insects which by favour 

 of climatic or other influences elude their checks and become abun- 

 dant. 



It is unfortunately not so clear how to encourage birds to in- 

 crease ; clearly, to increase the numbers of insect-feeding ones one 

 must also increase the food and the most we can do is to see that they 

 are not checked and that in every locality there are as many birds 

 as the insect supply will feed, i.e., these birds require only protection. 

 In the case of the King-Crow especially, I would extend the practice 



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