I.] THE DURATION OF LIFE. 1 9 



rudimentary, while the male possesses perfectly developed 



wmgs. 



The causes which have regulated the length of life in these 

 cases are obvious enough, yet still more striking illustrations 

 are to be found among insects which live in colonies. 



The duration of life varies with the sex in bees, wasps, ants, 

 and Termites : the females have a long life, the males a short 

 one ; and there can be no doubt that the explanation of this 

 fact is to be found in adaptation to external conditions of life. 



The queen-bee — the only perfect female in the hive— lives 

 two to three years, and often as long as five years, while the 

 male bees or drones only live four to five months. Sir John 

 Lubbock has succeeded in keeping female and working ants 

 alive for seven years — a great age for insects ^ — while the 

 males only lived a few weeks. 



These last examples become readily intelligible when we 

 remember that the males neither collect food nor help in 

 building the hive. Their value to the colony ceases with the 

 nuptial flight, and from the point of view of utility it is easy to 

 understand why their lives should be so short ^. But the case 

 is very different with the female. The longest period of repro- 

 duction possible, when accompanied by very great fertility, is, 

 as a rule, advantageous for the maintenance of the species. It 

 cannot however be attained in most insects, for the capability 

 of living long would be injurious if all individuals fell a prey to 

 their enemies before they had completed the full period of life. 

 Here it is otherwise : when the queen-bee returns from her 

 nuptial flight, she remains within the hive until her death, and 

 never leaves it. There she is almost completely secure from 

 enemies and from dangers of all kinds ; thousands of workers 

 armed with stings protect, feed, and warm her ; and in short 

 there is every chance of her living through the full period of 

 a life of normal length. And the case is entirely similar witli 

 the female ant. In neither of these insects is there any reason 

 why the advantages which follow from a lengthened period o'i 

 reproductive activity should be abandoned^. 



[^ Sir John Lubbock has now kept a queen-ant alive for nearly 15 

 years. See note i on p. 52. — E. B. P ] 



^ See Appendix, notes 7 and 9, pp. 60 and 64. 

 2 Ibid., note 6, p. 59. 



C 2 



