iv] DIPLOFTERA 51 



This process is repeated as the need arises, and entails 

 much labour on the " workers " : the material removed 

 from inside is used anew for construction of cells 

 or of the protecting envelopes. These last are very 

 numerous and hold between them layers of air : they 

 serve to prevent the escape of heat generated within 

 the nest. The temperature inside a strong nest is 

 between 85 F. and 90 F. 



As the nest is made larger the soil is removed 

 from the subterranean cavity in order to afford more 

 space. "Workers" may be seen issuing one after 

 another from the hole and carrying away load after 

 load of soil in their jaws. The exact shape of the 

 individual combs is normally circular ; but should an 

 immovable obstacle be encountered in the process of 

 excavation, the shape of the combs and of the whole 

 nest is adapted to meet the special circumstances. 



When the first comb has reached a convenient size 

 pillars of wasp-paper are built downwards from the 

 angles of some of the more central cells. At the 

 lower ends of these pillars a second tier of cells 

 similar to the first is added; and so on with each 

 successive tier as the strength of the colony demands. 

 An interval just sufficient to allow the wasps to move 

 freely about within the nest is left between each suc- 

 cessive comb, and also between their margins and the 

 innermost of the protective wrappings. In the central 

 portions of the combs the cells are very regularly 



42 



