124 A BOOK OF INSECTS 



ings of the same observer. It relates to a mason bee 

 (Clialicodoma vmraria), which constructs a nest of from 

 six to ten cells, using as material "a calcareous clay, 

 mixed with a little sand and kneaded with the mason's 

 own saliva." Each cell, when complete, is stored with 

 nectar and pollen. Then an egg is laid, and a roof is 

 added. Finally, the bee covers the whole group of cells 

 with a dome-shaped mass of its usual mortar. Now as 

 these nests are often built upon pebbles, they may readily 

 be moved from one place to another without injury ; and 

 by taking advantage of this fact Fabre was able to de- 

 monstrate by experiment that the bee, although she can 

 return unerringly from a distance of four kilometres to 

 her chosen nesting site, is quite unable to recognise her 

 own work. Further, he found that the operations of 

 building, storing and egg-laying succeeded one another 

 with automatic precision, without regard to circumstances. 

 " Here is a mason bee " (he writes) " at work on the first 

 course of her cell ; in exchange I give her one not only 

 completed, but half full of honey, which I stole from an 

 owner who would speedily have laid an egg there. What 

 will the mason do with this munificent gift which spares 

 her the labour of building and storage ? Leave her 

 mortar, of course, lay an egg, and close all up. Not at 

 all, the animal finds our logic illogical. The insect obeys 

 an inevitable, unconscious impulse. It has no choice as 

 to what it shall do — no discernment as to what is and is 

 not desirable — but glides, as it were, down an irresistible 

 slope prepared for it beforehand to bring it to a deter- 

 mined end. The facts still to be stated affirm this 

 strongly. The bee, which is building, and to which I 

 oiler a cell ready made and full of honey, will not give up 

 building for that : she is following her trade as mason, 

 and once on that tack, led on by unconscious impulse, 



