INTRODUCTION. 11 



indefatigable republics. Our own docks and em- 

 bankments have been threatened by such minute 

 ravagers. 



The enormous injuries which insects cause to man 

 may thus be held as one reason for ceasing to considei 

 the study of them as an insignificant pursuit ; for 

 a knowledge of their structure, their food, their 

 enemies, and their general habits, may lead, as it 

 often has led, to the means of guarding against their 

 injuries. At the same time we derive from them 

 both direct and indirect benefits. The honey of the bee, 

 the dye of the cochineal, and the web of the silk-worm, 

 the advantages of which are obvious, may well be 

 balanced against the destructive propensities of in- 

 sects which are offensive to man. But a philosophi- 

 cal study of natural history will teach us, that the 

 direct benefits which insects confer upon us are even 

 less important than their general uses in maintaining 

 the economy of the world. The mischiefs which 

 result to us from the rapid increase and the activity 

 of insects, are merely results of the very principle by 

 which they confer upon us numberless indirect ad- 

 vantages. Forests are swept away by minute flies ; 

 but the same agencies relieve us from that extreme 

 abundance of vegetable matter, which would render 

 the earth uninhabitable, were this excess not periodi- 

 cally destroyed. In hot countries, the great business 

 of removing corrupt animal matter, which the vulture 

 and the hyaena imperfectly perform, is effected with 

 certainty and speed by the myriads of insects that 

 spring from the eggs deposited in every carcass, by 

 some fly seeking therein the means of life for her 

 progeny. Destruction and reproduction, the great 

 laws of Nature, are carried on very greatly through 

 the instrumentality of insects; and the same princi- 

 ple regulates even the increase of particular species 



