The Hunting Wasps 



ground, down which they have slipped when 

 the huntresses have momentarily left them, 

 for some reason or other. These Crickets 

 fall a prey to the Ants and Flies; and the 

 Sphex-wasps who come across them take 

 good care not to pick them up, for, if they 

 did, they would themselves be admitting ene- 

 mies into the house. 



These facts seem to me to prove that, 

 while the Yellow-winged Sphex' arithmetical 

 powers enable her to calculate exactly how 

 many victims to capture, she cannot achieve 

 a census of those which have safely reached 

 their destination. It is as though the insect 

 had no mathematical guide beyond an irre- 

 sistible impulse that prompts her to hunt for 

 game a definite number of times. When the 

 Sphex has made the requisite number of jour- 

 neys, when she has done her utmost to store 

 the captures that result from these, her work 

 is ended; and she closes the cell whether com- 

 pletely or incompletely provisioned. Na- 

 ture has endowed her with only those facul- 

 ties called for in ordinary circumstances by 

 the interests of her larvae; and, as these blind 

 faculties, which cannot be modified by ex- 

 perience, are sufficient for the preservation 

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