XI THE SCIENCE OF INSTINCT 149 



straight to its assassin. Now for it. Alas ! no ; 

 the Sphex continues to draw back, behaves like a 

 veritable coward, and finally takes wing. I never 

 saw her again. Thus ended to my confusion an 

 experiment which had so excited my enthusiasm. 



Later, and gradually, as I visited more burrows I 

 came to understand my want of success and the 

 obstinate refusal of the Sphex. I always, without 

 exception, found stored a female ephippiger with 

 an abundant and succulent store of eggs inside her. 

 This, it would seem, is the favourite food of the 

 larvae. In my rush among the vines I had laid 

 hands on one of the other sex. It was a male which 

 I offered to the Sphex ! More clear-sighted than I 

 in the great victualling question, she would have 

 nothing to say to my game. " A male ! Is that the 

 kind of dinner for my larvae ? And, pray, for whom 

 do you take them ? " How sensitive must be these 

 dainty eaters who appreciate the difference between 

 the tender flesh of the female and the comparatively 

 dry body of the male ! What a penetrating glance 

 which can distinguish instantly the one sex from the 

 other, though alike in form and colour ! The female 

 has an ovipositor to bury her eggs with, and this is 

 almost the only outward difference between her and 

 the male. This difference never escapes the keen- 

 sighted Spex, and that is why my experiment made 

 her rub her eyes, immensely puzzled by a prey with- 

 out an ovipositor, which she was perfectly sure had 

 one when it was caught. At such a transformation 

 what must have passed in her little Sphex brain ? 



Now let us follow her when, the burrow being 

 ready, she returns to find her victim, deserted not 



