172 INSECT LIFE xn 



some predatory Hymenoptera are careful when 

 obliged to suspend work to defend the mouth of 

 their burrow by closing it up temporarily. I have 

 seen certain Ammophilae, whose burrow is a vertical 

 well, close the entrance with a little flat stone 

 when the insect goes a -hunting, or stops mining 

 when the hour to leave off work comes at sunset. 

 But in that case the stoppage is slight — a mere slab 

 set on the top of the well. It takes but a moment 

 when the insect comes to displace the little flat stone, 

 and the door is open. But what we have just seen the 

 Sphex construct is a solid barrier — strong masonry, 

 where layers of alternate dust and gravel occupy 

 the whole passage. It is definitive, and no tem- 

 porary work, as is sufficiently shown by the careful 

 way in which it is constructed. Besides, as I think 

 I have already proved, it is very doubtful, consider- 

 ing the manner in which she acted, whether the 

 Sphex would return to use the dwelling which she 

 had prepared. A new ephippiger will be caught else- 

 where, and elsewhere too will the storehouse destined 

 for it be hollowed. As, however, these are but con- 

 clusions drawn by reasoning, let us consult experi- 

 ment, more conclusive here than logic. I let nearly 

 a week pass in order to allow the Sphex to return 

 to the burrow so methodically closed, and use it if 

 she liked for her nest-laying. Events answered to 

 the logical deduction ; the burrow was just as I had 

 left it, well closed, but without food, egg, or larva. 

 The demonstration was decisive ; the Sphex had 

 not returned. 



Thus we see the plundered Sphex go into her 

 house, pay a leisurely visit to the empty chamber, 



