in PSITHYRUS, THE USURPER-BEE 63 



she had lost the scent she returned at once to search 

 again inside. 



The Psitkyrus is much more likely to find a 

 nest if the tunnel leading to it is short than if it 

 is long. Most of the nests containing Psithyri 

 that I have dug up had tunnels not exceeding 

 fifteen inches in length, and in none were they over 

 two feet. It is probably to escape the Psitkyrus 

 that lapidarius and terrestris nests often have 

 longer tunnels than those of any other species. 



In her wanderings the Psitkyrus may find and 

 enter the nest of some other species of Bombus. 

 Having succeeded in making herself acceptable to 

 the inhabitants, she becomes a temporary lodger 

 in this nest, making it her headquarters and re- 

 turning to it for meals and also to pass the night. 

 I once found a Ps. rupestris queen lodging in a weak 

 nest of B. agrorum in the thatch of a cow-lodge ; 

 another rupestris was a frequent visitor in a nest 

 of B. derhamellus I had under observation in June 

 1 9 10, where she was supported by the queen only, 

 no workers having yet emerged. I found a Ps. 

 vestalis lodging with a B. derhamellus queen on 

 June 9, 19 10. ' On June 10, I found a Ps. vestalis 

 in a nest of B. pratorum with the queen and 

 seven workers ; and on July 4, I discovered a Ps. 

 vestalis in a nest of B. pratorum containing the 

 queen and twenty workers. I have never found 

 a Psitkyrus lodging in a populous nest. 



The majority of the Psitkyrus queens discover 

 the nests of their victims when only the first batch 



