in PSITHYRUS, THE USURPER-BEE 67 



another's presence when they have eggs to lay. 

 Whether the jealousy is mutual, whether the 

 Psithyrus is the aggressor, or whether the Bombus 

 queen compasses her own destruction by first 

 attacking the Psithyrus, it is impossible to say. In 

 the above case, only three hours before I discovered 

 that the death of the queen had occurred, I looked 

 into the nest and saw both queens on the comb, and 

 there was nothing in their behaviour towards one 

 another to indicate the approaching tragedy. On 

 the whole, I think it probable that the Bombus queen 

 starts the fight as soon as she discovers that the 

 Psithyrus is about to lay, an unpardonable fault in a 

 member of her household at this early stage. 



I believe that a Psithyrus queen never commences 

 laying as soon as she enters the nest of her host, and 

 that egg-production is the result of living in luxury 

 in the nest for some days. Indeed, there is every 

 reason to suppose that if the colony when discovered 

 by the Psithyrus is in too early a stage, or too 

 struggling a condition, the development of eggs 

 in the Psithyrus, and, consequently, the murder of 

 the Bombzis, are delayed until the requisite degree 

 of prosperity is reached. 



The poor Bombus queen appears to have no 

 chance of victory over the well-armed Psithyrus. 

 I have taken a great many nests of lapidarius and 

 terrestris in all stages, but have seen no evidence 

 to show that the Bo??ibus queen ever succeeds in kill- 

 ing the Psithyrus, or that she ever escapes being 

 destroyed by the latter. Here, however, my 



