292 HYMENOPTERA 



when she leaves it. The moment she has gone, up hurries 

 one of the Idia flies and attempts to get through the 

 barrier. Sitting ahnost upright on the end of the abdo- 

 men, the little fly throws the sand forwards with quick 

 movements of its legs, as if trying to burrow backwards 

 through the barrier. But I have never seen one accom- 

 plish more than making a slight dimple in the loose sand. 

 But quite often the careless Bembex has gone away leaving 

 the burrow open, and then the Idia has its chance. It 

 hurries up with such eagerness to get down the burrow 

 that it may be seen literally to tumble head over heels 

 as it scrambles down. There is need for hurry, for how 

 can it tell when the rightful owner will come back, and 

 then it may meet with very rough treatment ! But as 

 a matter of fact I have never seen Bemhex take any 

 notice of the mean little intruder, though it may some- 

 times actually be met at the mouth of the hole by the 

 returning huntress. Yet sometimes it does fall a victim 

 to the sharp sting, for among flies dug up from a burrow 

 I have found specimens of Idia. 



Small pink dipterous larvae that are found in the 

 burrows are probably Idia, though I was unsuccess- 

 ful in rearing them. It is, of course, possible that 

 they are not strictly enemies of Bemhex, even in an 

 indirect manner, by devouring the larva's food ; they 

 may merely feed on debris of legs and portions of bodies 

 left by the more fastidious Bembex larva. 



Every colony of Bembex, of those species that I have 

 seen, has had these little brown flies in attendance. Some 

 were sent to the British Museum, and I was informed 

 that the species was a new one, and this habit had not 

 previously been recorded for the genus. 



The first Bembex that I ever saw at work was B. cap- 

 ensis, which I found at Jinja in 1910. One was seen 

 going into the burrow carrying a full fed Tse-tse, whose 

 shining red, bloated abdomen full of blood was quite 



