CHAPTER IV 



THEIR RELATION TO EACH OTHER 



IT has been brought out, directly and incidentally, 

 that insects are among the most prolific animals. If all 

 the feeders on vegetable life were allowed to develop 

 absolutely without check during two successive years, 

 the first of them would see every green thing swept 

 from the face of the earth, and the second would destroy 

 all possibility of the future recurrence of fully 90 per 

 cent, of all the existing plants. And if during the same 

 period all forms feeding upon vertebrate life were 

 allowed to develop in the same way, our globe would 

 be a practically uninhabited and uninhabitable desert. 



But the very fact that they are so remarkably 

 fecund is an indication that they have many dangers 

 to contend with and many difficulties to surmount 

 before reaching the adult or reproductive stage. Under 

 normal conditions and in the long run, one pair of 

 moths, producing say 500 eggs, are represented next 

 year by another pair of the same species, and no more: 

 that is, out of 500 eggs, producing 500 caterpillars, 

 498 are destroyed in some way. Naturally this varies 

 from year to year to some extent, favorable conditions 

 permitting an increase one year and causing a decrease 

 at some other period. And, equally of course, while 

 some broods may be completely destroyed, others 

 may all come to maturity. 



Now the very fact that an insect exists at all, is 

 proof that it is adjusted to its surroundings, including 

 its parasitic and predatory enemies and all the other 

 natural checks. And when it occurs as an abundant 



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