ORDER IV.—MOTHS AND BUTTERFLIES. 129 
terous insects in existence in this country, and as each fe- 
male lays on an average 300 eggs, half their number, 
viz., 6000 females, will produce 1,800,000 caterpillars; in 
the second generation, 180,000,000; and in the third, 
27,000,000,000. 
If such an immense multiplication of so voracious an 
animal were to be continued without any check, man and 
beast would soon be destroyed by starvation; but it is un- 
doubtedly one of the designs of Nature that these should 
increase immensely for the very purpose of furnishing suffi- 
cient nourishment for the birds and other winged animals 
which make them their principal food. It is ascertained 
that a single robin or woodpecker, and many others of the 
warblers, carry every day about fifty grubs or caterpillars 
to their nests as food for themselves and their young. 
Now if there were only one million of these birds, of 
which each one devours 6000 caterpillars during the months 
of April, May, June, and July, by no means a large com- 
putation, the number of caterpillars and grubs thus de- 
stroyed will amount to 6,000,000,000 annually. 
Caterpillars are, therefore, of great use to us in furnish- 
ing so abundant food and nourishment for the birds, which 
enliven and embellish the country with their happy songs 
and their beautiful plumage, and which themselves supply 
us with a palatable and delicious article of food. 
Caterpillars are also destroyed by various kinds of vein- 
winged insects, principally by different species of the Ich- 
neumon fly, which with her ovipositor thrusts one or sever- 
al eggs into the body of the caterpillar, upon the flesh of 
which the maggots of these flies subsist, until they come out 
as perfect flies, of course destroying the larve upon which 
they feed. We can often see this process carried on upon 
the body of a potato-worm, when it is full grown, and just 
ready to change into a cocoon. It will be completely cov- 
ered with many hundred minute white silk-like bodies, which 
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