64 ELE, HUMBLE-BEE Ill 
of workers has emerged, and this is the most 
favourable time, for these early workers are less 
hostile to strange queens than are the workers that 
emerge later. If the Pszthyrus fails to find the nest 
until the workers have become numerous they set 
upon her with great fury, and, after some time, gener- 
ally succeed in killing her by stinging her in a 
vulnerable spot, as for instance in the neck. On 
June 20, 1894, I took a nest of B. derrestris in 
an unusually forward stage for this date, there 
being 50 workers, 6 males, 2 young queens, and a 
quantity of male and queen cocoons. In the hole 
were two dead Pszthyrus vestalis females, both 
perfectly denuded of hair, and 15 dead terrestris 
workers. Evidently the Pszthyrt had been killed, 
but only after severe fighting and heavy loss. Again, 
on July 14, 1911, I found the dead body of a Ps. 
vestalts, also absolutely hairless, lying in the grass 
at the mouth of the tunnel of a strong ¢errestris 
nest : the workers must have killed her and dragged 
her to the surface. 
It is, therefore, necessary for the Pszthyrus to find 
the nest before many workers are out, but it would 
not be to her advantage to kill the queen until the 
latter has laid the greater number of the worker 
eggs ; and, as a matter of fact, she does not do so. 
The Sombus queen, on first meeting the 
Psithyrus in her nest, shows a certain amount 
of agitation, and may advance to attack her, but, 
her courage failing, she draws back. The Pszthyrus, 
however, treats the queen with good-natured in- 
