DESTROYERS OF APHIDES. 107 



prey upon Aphides, but I have frequently observed when 

 the winged Aphis is caught in the spider's web, that the 

 spider has not attacked it. Whether this arises from his 

 having been surfeited with the great superfluity of this 

 kind of food this year, or whether he does not like the 

 flavor of them, I am at a loss to determine. 



(426.) Doubtless Aphides form dainty food to the soft- 

 billed birds, and if they would entirely live upon them, 

 they would doubtless devour three or four thousand at a 

 single meal. With regard to birds, however, a very impor- 

 tant question is opened for our consideration ; for if they 

 prefer the parasites of the Aphis to the Aphides themselves, 

 then their presence would be hurtful ; if, on the contrary, 

 they eat the Aphides and avoid the parasites, then they 

 would act most beneficially. 



(427.) When a schoolboy, I formed the idea of examin- 

 ing the crops of birds at various times of the day, and at all 

 seasons of the year, so as to ascertain the number of insects, 

 the kinds of insects, and all other kinds of food that they 

 devour. Compelled, however, to live in London, and 

 engaged in other matters, I ceased to pursue my plan, 

 though I saw facts amply sufficient to astonish me at the 

 vast collections of insects which the crops of birds contain. 



I would advise the farmer to shoot various birds where 

 the vastator abounds, and to examine their crops, to ascer- 

 tain whether they prefer the creatures themselves or the 

 parasites. 



(428.) Ducklings, which delight in eating little insects, 

 would also doubtless devour these destroyers of human 

 food. 



(429.) From the above observations, we find, that, 

 although our most valuable vegetables are threatened with 



