THE SOCIAL INSECTS 



since every worker which accompanies the queen has been 

 bred from a cell which might otherwise have produced 

 another queen. One hundred cells, at the end of the season, 

 might produce ten queens, ten males and eighty workers. 

 The males would fertilise the females and die, and ten swarms 

 of one queen and eight workers could be produced. On the 

 other hand, in the absence of swarming, something like fifty 

 males and queens might have been produced, with the 

 potentiality of six times as many new colonies. The only 

 possible conclusion seems to be that swarming is advan- 

 tageous because the colony is at all times protected by a 

 number of workers. 



Owing to its small size, to the absence of an envelope, 

 and to the relatively exposed situation in which it is built, 

 the colony of Polistes cannot avoid being cooled at night. 

 In Europe, these wasps usually build the nest in a sheltered, 

 south-facing situation, so as to get the full heat of the sun, 

 and they have two effective methods of cooling it if it gets 

 too hot, as it sometimes does when the sun's rays fall directly 

 on it. In the first place they fan very vigorously with their 

 wings. If the temperature continues high, some of them 

 fetch drops of water which they put into the cells. The 

 fanning is continued and the nest is cooled by evapor- 

 ation. The nest may be maintained at 12 C below the 

 temperature of an unoccupied nest placed nearby for com- 

 parison. 



According to Deleurance, the cooling of the nest at night 

 plays an important part in determining whether a grub will 

 turn into a worker or a young queen. He had earlier shown 

 that in artificial conditions queen-producing eggs might be 

 laid and the grubs might even have spun their cocoons before 

 any workers had hatched, so that the developmental stage of 

 the whole colony does not seem to decide whether or not 



64 



