170 INSECT ARTIZANS AND THEIR WORK 



The warm air is kept in by the paper walls, and 

 radiation on cold nights is guarded against hy the 

 method of construction. The principle of the 

 down quilt and the woollen blanket had been 

 discovered by the wasp long before man adopted 

 these substitutes for the furry coats of the animals 

 he used to hunt. 



If you cut through the walls of a large wasp's 

 nest you will find there are several layers of paper 

 with air spaces between them. Imprisoned air 

 between layers of non-conducting material is one 

 of the most efficient means of maintaining an equal 

 temperature ; and the building of the vespiary 

 walls is evidently carried out with this principle 

 in view. 



In the early days of a Tree Wasp's nest, the um- 

 brella that is built as a shelter for the first three 

 or four cells is soon continued downwards as a 

 pear-shaped bottle with a mouth at the narrow 

 end. When a few workers are available they cover 

 this with additional wrappings, always with a space 

 between every two layers ; and right through the 

 season they are always adding more and more to 

 the exterior. If one could judge only by what is 

 seen from outside, he would imagine that the walls 

 had become excessively thick ; but all the time 

 that additions are being made to the exterior the 

 inner layers are being successively cut away to 

 allow of additions to the circumference of the 

 combs. In this way the nest is being constantly 

 enlarged without at any time exposing the interior. 



