32 INSECT ARCHITECTURE. 



out after a tower was completed. By raising a 

 tower of the materials which she excavates, the wasp 

 produces the same shelter from external heat, as a 

 human creature would who chose to inhabit a deep 

 cellar of a high house. She further protects her 

 progeny from the ichneumon fly, as the engineer con- 

 structs an outwork to render more difficult the ap- 

 proach of an enemy to the citadel. Reaumur has seen 

 this indefatigable enemy of the wasp peep into the 

 mouth of the tower and then retreat, apparently 

 frightened at the depth of the cell which he was 

 anxious to invade. 



The mason-wasp does not furnish the cell she has 

 thus constructed with pollen* and honey, like the 

 solitary bees, but with living caterpillars, and these 

 always of the same species, — being of a green colour, 

 and without feet. She fixes the caterpillars together 

 in a spiral column: they cannot alter their position, 

 although they remain alive. They are an easy prey 

 to their smaller enemy; and when the grub has eaten 

 them all up, it spins a case, and is transformed into 

 a nymph, which afterwards becomes a wasp. The 

 number of caterpillars which is thus found in the 

 lower cavity of the mason-wasp's nest is ordinarily 

 from ten to twelve. The mother is careftil to lay in 

 the exact quantity of provision which is necessary to 

 the growth of the grub before he quits his retreat. 

 He works through his store till his increase in this 

 state is perfected, and he is on the point of under- 

 going a change into another state, in which he re- 

 quires no food. The careful purveyor, cruel indeed 

 in her choice of a supply, but not the less directed 

 by an unerring instinct, selects such caterpillars as 

 she is conscious have completed their growth, and 

 will remain thus imprisoned without increase or cor- 



* The prolific powder of flowers. 



