iv PREFACE. 
has been killed because he picked up a few grains or 
ate a small quantity of fruit, when he really was of 
great service to the farmer or gardener, because he 
devoured daily a large number of worms, the grain 
or the fruit being a very small portion of his food. 
A war was year after year waged by every cotton- 
grower against an insect which was supposed to be 
very destructive to the plant. But after a while it 
was discovered that a great mistake had been made— 
that another smaller insect did the mischief, and that 
the one which had been destroyed in such great num- 
bers was really the cotton-grower’s friend, for it lived 
by preying upon this smaller insect. One example 
more shall suffice, although great numbers of a similar 
character might be cited. It is stated by Buffon that 
there was once great danger that the island of Bour- 
bon would be entirely devastated by locusts, but it 
was saved from this.catastrophe by the knowledge 
which the governor had of a fact in Natural History. 
He happened to know that a bird in India, called the 
Grakle, was of great service in destroying the eggs 
and grubs of these insects, and he therefore had a 
large number of pairs of this bird imported into the 
island. They multiplied rapidly, and in a few years 
the locusts were exterminated. But now the grakles, 
their natural food having given out, fell to digging 
up and eating the seeds sown in the ground. The 
people thereupon were aroused against them, and 
even obtained the enactment of a law for their exter- 
mination. But in a few years they saw their error, 
for the locusts largely increased again. A new sup- 
ply of grakles was obtained, and their preservation 
was secured by very rigid enactments. So high were 
