43 [Vol. xli. 



gone long before the protection laws came to the rescue o£ 

 the comparative few that remained. 



Another great reason adduced for protecting birds is their 

 usefulness as destructors of insects ; but even here the use- 

 fulness of birds may be exaggerated — all insects are seasonal, 

 only appearing in certain stages for a short time in tlie 

 year, — so that if a species of Bird is to be effective, it must 

 not only be present when the insect is in the particular stage 

 in which the Bird eats it, but the Bird must either migrate 

 or turn its attention to other food during the rest of the 

 year. Take, for instance. Thrushes, who may do a consider- 

 able amount of good by destroying snails, but they have now 

 become so numerous that the damage they do to fruit in 

 season far more than counterbalances the good that they 

 may do at other times. 



Then, again, all insects are not injurious, and the number 

 of species of birds that restrict their diet to one kind of 

 insect is very small, so that in protecting an insectivorous 

 bird we may be protecting the enemy of a very injurious 

 insect. For instance, spiders are tit-bits to any insectivorous 

 bird, yet they are the most efficient destructors of flies that 

 are universally acknowledged to be noxious and dangerous 

 to ourselves. 



Therefore^ birds are at the best, merely aids, as the natural 

 enemies of many insects, in destroying a proportion of them ; 

 but, on the ground of our first law, they will never come 

 anywhere near exterminating them, much less exterminating 

 any particularly noxious species. When it is necessary to 

 destroy insects, other and artificial means have proved the 

 best — to mention two cases. Mosquitoes and Flies. The 

 former, as is well-known, have been entirely eliminated in 

 some districts by draining the land or spreading a thin film 

 of oil over ponds or marshes, while flies have been largely 

 reduced by the removal of refuse and rubbish heaps and 

 greater general cleanliness. Both these methods agree with 

 the third law in the destruction of breeding-places. 



These methods have been found quite as efficacious and 



