172 A BOOK OF INSECTS 



suffice to illustrate this point. A single grey flesh-fly 

 {Sarcophaga carnaria) is capable of producing 20,000 

 larva?. " Each of these larvae " (writes Dr. Wallace in 

 Darwinism) "remains in the pupa state for about five or 

 six days, so that each parent fly may be increased ten 

 thousand-fold in a fortnight. Supposing they went on 

 increasing at this rate during only three months of summer, 

 there would result one hundred millions of millions of 

 millions for each fly at the commencement of summer 

 — a number greater, probably, than exists at any one 

 time in the whole world." Thus, while the protective 

 devices with which we have dealt can only succeed in 

 a minority of cases, the abounding fecundity of the insect 

 always remains to safeguard the continuance of the race. 



