The Mason-bees 



Besides, it Is the one favourable moment 

 for the Dioxys. If she waits for the Mason- 

 bee to lay, it is too late, for the parasite is 

 not able to break down doors, as the Stelis 

 does. As soon as her egg is laid, the Mason- 

 bee of the Sheds comes out of her cell and at 

 once turns round and proceeds to close it up 

 with the pellet of mortar which she holds 

 ready in her mandibles. The material is em- 

 ployed with such method that the actual seal- 

 ing is done In a moment; the other pellets, the 

 object of repeated journeys, will serve merely 

 to increase the thickness of the lid. The 

 chamber is Inaccessible to the Dioxys from 

 the first touch of the trowel. Hence it Is ab- 

 solutely necessary for her to see to her egg 

 before the Mason-bee of the Sheds has dis- 

 posed of hers and no less necessary to conceal 

 it from the Mason's watchful eye. 



The difficulties are not so great in the nests 

 of the Mason-bee of the Pebbles. After this 

 Bee has laid her egg, she leaves It for a time 

 to go in search of the cement needed for clos- 

 ing the cell; or, if she already holds a pellet 

 in her mandibles, this is not enough to seal 

 it properly, as the orifice is larger. More 

 pellets are needed to wall up the entrance en- 

 260 



