The Yellow-winged Sphex 



preliminary descent of the burrow is of such 

 imperious necessity. 



Here is the only fact observed by myself 

 that may throw a little light on the problem. 

 Amid a colony of Sphex-wasps in full swing, 

 a colony from which any other Wasp is 

 usually excluded, I one day surprised a hunt- 

 ress of a different genus, Tachytes nigra, 

 carrying one by one, without hurrying, in the 

 midst of the crowd where she was but an in- 

 truder, grains of sand, bits of little dry stalks 

 and other diminutive materials to stop up a 

 burrow oiP the same shape and width as the 

 adjacent burrows of the Sphex. The labour 

 was too carefully performed to allow of any 

 doubt of the presence of the worker's egg in 

 the tunnel. A Sphex moving about uneasily, 

 apparently the lawful owner of the burrow, 

 did not fail, each time that the strange Wasp 

 entered the gallery, to rush in pursuit of her; 

 but she emerged swiftly, as though fright- 

 ened, followed by the other, who impassively 

 continued her work. I inspected this bur- 

 row, evidently an object in dispute between 

 the two Wasps, and found in it a cell pro- 

 visioned with four Crickets. Suspicion al- 

 most makes way for certainty: these pro- 

 visions are far in excess of the needs of a 

 73 



