INSECT SOCIETIES 



merely a modification of behaviour to meet the difficulties 

 of our winter climate, since colonies of some tropical species 

 disperse after a comparable developmental cycle. 



The termites, owing to the nature of their sex-determining 

 mechanism, at all times produce males and females in equal 

 numbers. It is probable that in them the sterilisation of most 

 individuals of each sex must have developed very early in 

 their history. 



The Hymenoptera, the group of which ants, bees and 

 wasps form a part, normally have a type of sex-determination 

 which makes it possible for purely female broods to be 

 produced for long periods. Once a female has mated the 

 actual fertilisation of each egg is under nervous control by 

 the female, and normally only unfertilised eggs will produce 

 males. While this might be expected to lead to a colony 

 rather different from that of the termites, the problems to be 

 solved are much the same. 



In solitary bees,and wasps, unfertilised females do not seem 

 to make nests, though there is still a large field here for 

 experimental study. On the other hand, fertilised egg-laying 

 females are commonly quarrelsome and tend to interfere 

 with each other's egg-laying. Thus the sterilisation of most 

 of the females without depriving them of the urge to work 

 must in most species have occurred quite early. Moreover, 

 since unfertilised eggs will develop into males, merely to 

 deprive the female offspring of the queen mother of their 

 opportunity to mate does not prevent reproduction. 



In the colonies of Polistes wasps it seems that the pre- 

 vention of egg-laying is still a mainly psychological in- 

 hibition. In the more advanced social species, the sterilisation 

 of the workers has gone much further, though egg-laying 

 can still occur, at least occasionally or in some individuals. 



Sterilisation might be described as the least wasteful way 



i95 



