MASON-BEES. 27 



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 pupa, 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 careful 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 undergoing a change into another state, in 

 which he requires 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 corruption till their 

 destroyer has gradually satisfied the necessities of his 

 being. "All that the worm of the wasp," says Eeamur, 

 " has to do in his nest, from his birth to his transformation, 

 is to eat." There is another species of wasp which does 

 not at once enclose in its nest all the sustenance which its 

 larva will require before transformation, but which from 

 time to time imprisons a living caterpillar, and when that 

 is consumed, opens the nest and introduces another.* 



Mason-Bees. 



It would not be easy to find a more simple, and, at the 

 same time, ingenious specimen of insect architecture than 

 the nests of those species of solitary bees which have been 

 justly called mason-bees (^Megachile, Latreille). Eeaumur, 

 who was struck by the analogies between the proceedings 

 of insects and human arts, first gave to bees, wasps, and 



* The prolific powder of flowers. 



t Bonnet, Contemplation, &e. 1. xii. c. 41. 



