XII THE IGNORANCE OF INSTINCT 177 



be certain whether S. flavipennis, which makes several 

 calls at the bottom of the same passage, and heaps 

 several grasshoppers in each, commits the same 

 irrational mistakes when accidentally disturbed. A 

 cell may be closed, although empty or imperfectly 

 stored, and yet the Sphex will return to the same 

 burrow to make others. Yet I have reason to believe 

 that this Sphex is subject to the same aberrations 

 as her two relations. The facts on which I base 

 my belief are these. When the work is completed, 

 there are generally four grasshoppers in each cell, 

 but it is not uncommon to find three or only 

 two. Four appears to me the usual number — first, 

 because it is the most frequent, and secondly, when 

 I have brought up young larvae dug up when eating 

 their first grasshopper, I found that all, even those 

 only provided with two or three, easily finished 

 those offered, up to four, but after that they hardly 

 touched the fifth ration. If four grasshoppers are 

 required by the larva to develop fully, why is it 

 sometimes only provided with three or even only 

 two ? Why this immense difference in the amount 

 of food ? It cannot be from any difference in the 

 joints served up, since all are unmistakably of the 

 same size, but must come from losing prey on the 

 road. In fact, one finds at the foot of the slopes 

 whose upper parts are occupied by Sphegidae, grass- 

 hoppers killed, and then lost down the incline, when, 

 for some reason or other, the Sphex has momen- 

 tarily left them. These grasshoppers become the 

 prey of ants and flies, and the Sphex who finds 

 them takes good care not to pick them up, as they 

 would take enemies into the burrow. 



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