8 FLASHLIGHTS ON NATURE 



and since each new aphis instantly begins to fix 

 its proboscis into the soft leaf-tissue, and in turn 

 to bud out other broods of its own, you need not 

 wonder that your favourite roses are so quickly 

 covered with a close layer of blight in genial 

 weather. 



To say the truth, the rate of increase in aphides 

 is so incredibly rapid, that one dare hardly mention 

 it without seeming to exaggerate. A single in- 

 dustrious little green-fly, which devotes itself with 

 a quiet mind to eating and reproduction, may easily 

 within its own lifetime become the ancestor of some 

 billions of great-grandchildren. It is not difficult 

 to see why this should be so. The original parent 

 buds out little ones from its own substance at a 

 prodigious rate ; and each of these juniors, reach- 

 ing maturity at a bound, begins at once to bud out 

 others in turn, so that as long as food and fine 

 weather remain the population increases in an 

 almost unthinkable ratio. Of course, it is the ex- 

 treme abundance of food and the ease of living 

 that result in this extraordinary rate of fertility ; 

 the race has no Malthus to keep it in check each 

 aphis need only plunge its beak into the rose-shoots 

 or leaves and suck ; it can get enough food without 

 the slightest trouble to maintain itself and a nume- 

 rous progeny. It does not move about recklessly, 

 or use up material in any excessive intellectual 

 effort ; all it eats goes at once to the production 

 of more and more aphides in rapid succession. 



Many things, however, conspire to show that 



