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 



