The Bumble-Bee Fly 



cell, the little creature is seized by the owner, 

 the Wasp-grub, which nabs it and turns and 

 returns it between its mandibles. Is this a de- 

 fensive bite? No, the Wasp-grub has merely 

 blundered, taking its visitor for a proffered 

 mouthful. There is no great harm done. 

 Thanks to its suppleness, the little grub 

 emerges from the grip intact and continues its 

 investigations. 



It might occur to us to attribute this tole- 

 rance to some lack of penetration in the Wasps' 

 vision. What follows will undeceive us: I 

 place separately, in empty cells, a grub of 

 Saperda scalaria and a Volucella-grub, both 

 of them white and selected so as not to fill the 

 cell entirely. Their presence is revealed only 

 by the paleness of the hind-part which serves 

 as a plug to the opening. A superficial ex- 

 amination would leave the nature of the re- 

 cluse undecided. The Wasps make no mis- 

 take: they extirpate the Saperda-grub, kill it, 

 fling it on the dust-heap; they leave the Volu- 

 cella-grub in peace. 



The two strangers are quite well recognized 

 in the secrecy of the cells: one is the intruder 

 that must be turned out; the other is the regu- 

 lar visitor that must be respected. Sight helps, 

 for things take place in the daylight, under 



273 



