IX ADVANCED THEORIES 121 



but such an extension of hunting ground cannot be 

 supposed for the Sphex, which I have found so faith- 

 ful to one exclusive prey, invariable for each species, 

 and which, moreover, finds among the Orthoptera 

 kinds of very different shapes. I have, however, 

 had the good fortune to meet with one case — only 

 one — of complete change in the larva's food, and 

 I mention it the more willingly in the archives of the 

 Sphegidai because such facts, scrupulously observed, 

 will one day be corner-stones for him who may 

 desire to build the psychology of instinct on solid 

 foundations. 



This is my fact. The scene is on a jetty by the 

 Rhone. On one side is the great river, with its 

 thunder of waters, on the other, a dense thicket of 

 osiers, willows, and reeds, and between the two a 

 narrow path with a bed of fine sand. A yellow- 

 winged Sphex appears, hopping and dragging its 

 prey along. What do I see ! It is no grasshopper, 

 but a common Acridian ! And yet the Hymen- 

 opteron really is the Sphex so well known to 

 me (S, flavipennis), the energetic huntress of grass- 

 hoppers ! I can hardly believe my eyes. The 

 burrow is not far off; she enters and stores her 

 booty. I seat myself, determined to await a new 

 expedition — wait hours if need be to see if so 

 extraordinary a capture is repeated. Seated there 

 I occupy the whole width of the path. Two simple 

 conscripts come up, new-clipped, with that incom- 

 parable, automaton-look conferred by the first days 

 of barrack life. They are chattering together — no 

 doubt talking of their homes and the girls they left 

 behind them ; each is peeling a willow switch with a 



