INTRODUCTION 45 



are harmful and which useful to man, and, however 

 strange it may seem, this question is very far from being 

 entirely settled. We do not regard the matter from the 

 point of view of the hunter, who takes everything to be 

 harmful that menaces his safety, even if it is a question 

 of animals which are most useful in every other respect. 

 By harmful we mean only what is really injurious to 

 civilisation, or that restricts man's efforts, while 

 guarding ourselves against too narrow a view. Game, 

 for instance, does a lot of harm in the field and the 

 wood, but compensates us so richly with its flesh that 

 we readily overlook the mischief it does in the corn 

 or on the trees. The field-mouse is always mis- 

 chievous, and its enemies are useful to us. The chief 

 of these are the owls, which live almost entirely on 

 mice. But we might go further, and regard almost all 

 our birds of prey, except, perhaps, the hawk and 

 sparrow-hawk, as useful on account of their destruction 

 of mice. 



We can determine the food of birds of prey with 

 some confidence, but it is not so easy in the case of the 

 insectivorous birds. It is among insects that we find 

 the chief enemies of culture. There are the typographer- 

 beetle and the caterpillar of the processionary butterfly, 

 the pine lappet-moth and the black-arches all injurious 

 in the wood the swarm of grass-hoppers, and especially 

 the dreaded migratory locust that so often ravages the 

 fields. The cockchafer is equally injurious in its adult 

 state and when it is a young grub ; and whoever has 

 been in a wine-country knows what it means for the 

 dreaded phylloxera to get into the vineyards. But it 



