MAN AND THE WEB OF LIFE 89 



of farmer and gardener ; of a considerable number it must 

 be said that while they do harm they also do good, and that 

 the balance is in their favour ; of the vast majority it may be 

 safely said that they are beneficial. They are joys for ever 

 besides. 



The elimination of animals hostile to man or his interests 

 is often agreed upon as beyond all question desirable, but there 

 is very frequently a tax to pay. The extermination of 

 poisonous snakes is probably inevitable, but one must at 

 least be prepared for a multiplication of the mice and other 

 ;< vermin " on which many of the snakes normally fed. In 

 studying the influence of birds and other creatures on man's 

 material interests, one is continually confronted with the 

 difficulty of getting a " clear issue." Squirrels are destroyed 

 because they spoil so many young trees ; but the result is 

 an over-multiplication of wood-pigeons, on whose young squabs 

 the ordinarily vegetarian squirrel levies useful toll. 



6. Without any active elimination man may bring about 

 serious changes by what we may call discouraging certain 

 types. Thus the gradual extension of arable land, the gradual 

 paring away of the delightful wild corners, the drainage of 

 swamps, the clearing of golf-courses, and so on, are having a 

 rather dismal effect on our British fauna. Many interesting 

 types have sought remoter retreats or have left us altogether, 

 and the nemesis of cutting off the nesting-places of common 

 insectivorous birds has made itself felt in many places. One 

 hopes, however, that there is a fresh growth of a vivid and 

 determined awareness that creatures like bitterns and badgers 

 are national treasures of real value, not to be sacrificed any 

 longer either to ignorance or greed. 



7. Some of the most striking linkages are those concerned 

 in various diseases of man and his stock. Malaria is due to 

 a minute animal which lives in the red blood corpuscles of 

 man ; it passes into a mosquito (Anopheles maculipennis) 

 that sucks man's blood ; after complicated changes in the 

 mosquito the microbe passes into the blood of another man 

 whom the insect bites. As the larval mosquito lives in pools 

 and breathes at the surface, it can be suffocated by a floating 



