THE STRUGGLE FOR LIFE 213 



Five hundred eggs would be a small average for fe- 

 males of the insect tribe. If all of these eggs were 

 to bring forth individuals and all these individuals and 

 their progeny were to continue the reproductive pro- 

 cess, how long would there be sustenance for such 

 myriads ? It has been estimated that if the eggs of 

 a common house-fly should develop and each of its 

 progeny should find the necessary condition for growth 

 and development, without loss or destruction, the people 

 of the city in which this might happen could not get 

 away soon enough to escape suffocation from an atmos- 

 phere filled with flies. Such conditions do not exist. 

 Why not ? Are there certain persons detailed from 

 each community to prevent undue multiplication ? 

 Evidently not. If all these forms were to appear the 

 food supply would soon be exhausted. The facts are 

 that the percentage of eggs which develop into mature 

 forms is very small. Unusually favorable conditions 

 sometimes occur to permit a goodly percentage of the 

 eggs to hatch and attain maturity. At such times we 

 have plagues. The multitudes of maple-worms and 

 grasshoppers which sometimes appear are illustrations. 

 But these are not of regular occurrence. Since, then, 

 all insects do not reach maturity, what determines 

 which ones shall succumb and which ones shall live ? 

 "All live who can." It is evident that there must be 

 strife for existence ; that among insect forms as well as 

 higher animal forms there is a struggle for existence, a 

 struggle which for the greater part is unconsciously 

 carried on by the individuals concerned. Some are 

 destroyed by mere accidents. Aside from this the 

 struggle takes place: (a) Between individuals of 



