in PSITHYRUS, THE USURPER-BEE 61 



poor orphans she creates to become her willing 

 slaves. 



The following are the details of the life-history 

 of Psithyrus rupestris and Ps. vestalis as I have 

 observed them : 



The queens hibernate solitarily in the ground 

 like the Bombus queens, but they do not quit their 

 winter quarters until after the Bombus queens have 

 emerged, and most of them are already engaged in 

 rearing their first batch of workers. 



Psithyrus rupestris much resembles her victim, 

 the lapidarius queen, in appearance, being about 

 the same size, and, like her, having a black coat 

 with a red tail ; but her wings are dark brown, not 

 clearly transparent as in lapidarius, and her flight 

 is feeble, producing a lower note than that of the 

 lapidarius queen, the rate of wing vibration being 

 slower. Ps. vestalis also rather resembles her 

 victim, B. terrestris, in her yellow band and whitish 

 tail, but is likewise distinguishable by her smoky 

 wings and soft low-sounding flight. 



But the most remarkable feature about the 

 Psithyrus queens is their exceedingly thick and 

 hard skin, covering them like a coat of mail and 

 protecting them from the stings of the Bombi. The 

 segments of the abdomen, in particular, are very 

 hard and lap tightly and closely over one another, 

 there being no wax-yielding membrane between 

 the dorsal segments, so that it is very difficult for 

 an adversary to force her sting between them. 

 Their coats are thin, perhaps as a compensation 



