The Mason-Wasps 



penter's. Her knack for wood-working, 

 moreover, is extremely useful in another 

 circumstance, as we shall see. The Three- 

 horned Osmia, also an enthusiastic parti- 

 tioner of reeds, does not employ this means 

 of obtaining a spacious lodging at small 

 cost, I find that she always leaves the first 

 party-wall intact, building the row of cells 

 against it, however short the section may be. 

 To make an opening in a slight barrier is 

 not one of her methods. She could do it 

 if she wished; for to gnaw through the ceil- 

 ing of the cell on hatching and then through 

 the general door of the nest is a more diffi- 

 cult job. She possesses in her mandibles a 

 tool powerful enough for the purpose; but 

 she is not aware that a splendid gallery lies 

 beyond the obstacle. How did the Odyne- 

 rus learn, if she did not know from the be- 

 ginning, what the Osmia, with her greater 

 experience of the reed, does not know? 



Apart from the ingenious device of 

 breaking down the party-wall in order to 

 enlarge the premises, the Odynerus is the 

 Osmia's equal as a plasterer and partition- 

 builder. The results of the two industries 

 resemble each other so closely that we 

 should easily confuse them if we merely ex- 

 amined the structure. We find in both 

 i88 



