210 CALCULATIONS. 



consume less than five hundred caterpillars in the course 

 of the day. The quantity destroyed in thirty days, at 

 this rate, by one nest would amount to fifteen thousand. 

 Suppose every square league of territory contained one 

 hundred nests of this species, there would be destroyed 

 by them alone in this space a million and a half of cater- 

 pillars in the course of one month. 



I was sitting at a window one day in May, when my 

 sister called my attention to a Golden Eobin in a black- 

 cherry tree employed in destroying the common hairy 

 caterpillars that infest our orchards, and we counted the 

 number he killed while he remained on the branch. Dur- 

 ing the space of one minute, by a watch, he destroyed 

 seventeen caterpillars. I observed that he did not swal- 

 low the whole insect. After seizing it in his bill, he set 

 his foot upon it, tore it asunder, and swallow^ed an atom 

 taken from the inside. Had he eaten the whole cater- 

 pillar, three or four would probably have satisfied his 

 appetite. But the general practice of birds that devour 

 hairy caterpillars is to eat only a favorite morsel. Hence, 

 they require a greater number to satisfy their wants. 



This fact led me to consider how vast an amount of 

 benefit this single species must contribute to vegetation. 

 Suppose each bird to pass twelve out of the twenty-four 

 hours in seeking his food, and that one hour of this time 

 is employed in destroying caterpillars. At the rate of 

 seventeen per minute, each bird would destroy a little more 

 than one thousand caterpillars daily while they were to 

 be found. Yet, if the crop of the bird were dissected, it 

 would not be possible to discover from these titbits the 

 character of the insect which he had devoured. So I 

 draw the inference that while we may discover many 

 important facts by dissection, all are not revealed to us 

 by this mode of examination. Imagine, however, from the 

 facts which I have recounted, the vast increase of cater- 



