290 HYMENOPTERA 



There is a shrill buzz, like a scream, from the fly as 

 it is caught and stung, and then the Bembex is seen to 

 be holding the fly closely to her abdomen between the 

 thighs of her hind legs, and darts away to her burrow. 



Sometimes the Bembex pounces on a fly as it sits on 

 my clothes, and I am able actually to see her sting it. 



Arriving at her burrow, Bembex alights at the exact 

 spot, and without a moment's hesitation, still holding 

 her prey between her legs, opens up the burrow and 

 passes in. 



Almost immediately she emerges again and repeats 

 the chase. On March 13th I thus watched one worker 

 for three and a quarter hours, during which she caught 

 twenty-nine Tse-tse and two other flies. The last four 

 Tse-tse had been caught and carried into the burrow in 

 five minutes. After this she finally closed the burrow 

 and flew away, and I, with great difficulty in the loose 

 sand, found the chamber at the end of the burrow and 

 took out all the flies that had been collected, and the 

 legless white grub, full grown. 



There were thirty-one Tse-tse flies and one other fly. 

 About half a dozen of them were dried and some partially 

 eaten. Twenty-one were males and ten females, eight 

 of which were fat ones containing a larva ; this is a very 

 high percentage of pregnant flies, for out of ninety-six 

 female flies that had been caught by my boys that 

 morning only 22 per cent, contained large larvae. 

 So that the Bembex had definitely selected the fattest 

 flies she could find in default of full fed individuals, which 

 are heavier on the wing and easier to catch. 



Another specimen was seen to catch six Tse-tse and 

 several other flies in an hour ; if, after close examination, 

 8he found no suitable Tse-tse on me, she would fly away 

 and return with other flies, though once she came with 

 a Tse-tse caught elsewhere. 



The burrow of another that was dug up, about eight 



