162 OUR BIRD ALLIES. 
way of insect destruction. On this computation, we 
find that 1,680,000 caterpillars would thus be destroyed, 
during those ten weeks only, upon each square mile 
of ground. And as, in the United Kingdom, there 
are at present 34,765 square miles of arable land, we 
have a total of 58,405,200,000 caterpillars, all more 
or less destructive, killed by sparrows while the various 
crops are at the most critical stage of their growth. 
And it must be borne in mind that an insect, 
during the larval or caterpillar stage of its develop- 
ment, eats an amount of food almost incredible in 
comparison with its bodily size and weight. Almost 
the whole of the interior of the body, indeed, is occu- 
pied by the digestive organs, and the life of the insect, 
during this period of its existence, is little more than 
one prolonged meal. It has been calculated, for 
instance, that a caterpillar, one month after birth, 
shas increased to nearly ten thousand times its original 
weight on leaving the egg, and has devoured mean- 
while no less than forty thousand times that weight 
in food. And the majority of caterpillars remain as 
such for considerably more than a month, their daily 
allowance of food, of course, increasing in proportion 
to their growth, until it almost passes the bounds of 
belief. 
Now let us consider what a terrible quantity of 
human produce, of one kind or another, these 
58,405,200,000 caterpillars would devour, were they 
permitted to live on until the natural close of their 
career. Also, in what greatly-increased numbers 
they would make their appearance in the following 
