THE SOCIAL INSECTS 



such as those producing a queen or a worker, have been 

 evolved, the actual trigger which sets off the individual on 

 one or other path may change. It is conceivable that even 

 if temperature now controls the development of queen or 

 worker in some Polistes it was something else which had 

 this effect originally. 



There are really two problems: first what is the evolu- 

 tionary advantage of having a worker caste? Second, what 

 mechanism leads to the production of workers at the present 

 day ? The advantages are fairly certain, namely a more 

 accurate control of egg-production and the release of energy 

 from that process for the other needs of the colony. The 

 mechanism of the development of the two types is much less 

 certain and need not be the same in every species. 



Most species of social wasps live in the tropics, and species 

 like the common wasp or the European Polistes, though 

 extensively studied, are really exceptions. It is probable that 

 the primitive and simpler arrangement is to have a colony 

 with several queens, with workers very little differentiated, 

 with no queen-hibernation but with colonies breaking up 

 into swarms. 



The life-cycle of the common wasp, with annual colonies 

 and hibernating queens, seems to be a modification for a 

 temperate climate. One very important feature is the 

 inhibition of the young queen's ovary in the autumn. The 

 quantity of food which the queen takes before the winter is 

 mostly laid down as fat to sustain her during hibernation. 

 In the spring, however, a similar process of feeding leads to 

 egg-development instead. This looks much more like a 

 special device for meeting the unfavourable climate than an 

 original feature of social life. The common wasp seems to 

 be much more firmly attached to temperate conditions than 

 is Polistes, and if they are both regarded as invaders from 



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