in PSITHYRUS, THE USURPER-BEE 65 



difference, unless the latter becomes disagreeably 

 aggressive, and then all she does is to lift occasion- 

 ally a warning leg, or to creep away and hide 

 herself like a coward in the nest material. If the 

 workers attack her, she tries to rub them off with 

 her legs, and slips into a crevice between the 

 clusters of cocoons, or into the nest material ; but, 

 protected by her coat of mail, she has little 

 cause to fear getting stung. 



Although the Psithyrus during the first few days 

 flies occasionally to and from the nest, I have seen 

 no evidence that she brings home any food, or that 

 she helps in any way to rear the Bombus brood. 

 Her first care is to ingratiate herself with the 

 inhabitants, and in this she succeeds so well that 

 the workers soon cease to show any hostility 

 towards her. Even the queen grows accustomed 

 to the presence of the stranger, and her alarm 

 disappears, but it is succeeded by a kind of de- 

 spondency. Her interest and pleasure in her brood 

 seem less, and so depressed is she that one can 

 fancy she has a presentiment of the fate that awaits 

 her. It is by no means a cheerful family, and the 

 gloom of impending disaster seems to hang over it. 



But while the queen grows more dejected, the 

 Psithyrus grows more lively, and takes an increasing 

 interest in the comb, crawling about over it with 

 unwonted alacrity, and examining it minutely. 



In June 1908 I had a good opportunity of 

 watching a Ps. rupestris establish herself in one 

 of my nests of B. lapidarius that I had placed in 



