XX MASON BEES 287 



surface of the nest, where the cells are hidden below 

 the old general mortar covering, new ones are built 

 as required. They are placed more or less horizontally, 

 one beside another, with no kind of order. Every 

 constructor builds as the fancy takes her, where and 

 as she wills ; only she must not interfere with her 

 neighbour's work, or rough treatment will soon call 

 her to order. The cells accumulate in chance 

 fashion in this workyard, where there is no general 

 plan whatever. Their form is that of a thimble 

 divided down the axis, and their enclosure is com- 

 pleted either by adjacent cells, or the surface of the 

 old nest. Outside they are rough, and look like 

 layers of knotted cords corresponding to the layers 

 of mortar. Inside the walls are level but not 

 smooth ; a cocoon will replace the absent polish. 



As soon as a cell is built it is stored and walled 

 up, as we have seen with Chalicodoma muraria. This 

 work goes on through the whole of May. At 

 length all the eggs are laid, and the bees, without 

 any distinction as to what does or does not belong 

 to them, all set to work on a common shelter of the 

 colony — a thick bed of mortar, filling up spaces and 

 covering all the cells. In the end the nests look 

 like a large mass of dry mud — very irregular, arched, 

 thickest in the middle, the primitive kernel of the 

 establishment, thinnest at the edges, where there are 

 fewest cells, and very variable in extent, according 

 to the number of workers, and consequently to the 

 time when the nest was begun. Some are not much 

 larger than one's hand, while others will occupy the 

 greater part of the edge of a roof, and be measured 

 by square yards. 



