232 lOcloher, 



None o£ our other common Bomhi are so bold as to do this, except 

 Sometimes B. lapidarius (also a pollen-sforer). The ordinary honey- 

 bee quietants, such as smoke and carbolic acid, do not seem to have 

 any effect on these Botnbi, and I have found that nothing less than 

 the deadly fumes from a rag soaked in a solution of cyanide of 

 potassium will reduce a strong nest of terrestris to order sufficiently 

 to enable one to examine it. 



Another very interesting jjoint of difference between the pouch- 

 makers and the polleti-sforers is the extent to which each are preyed 

 upon by the closely allied inquiline genus Psithi/rus, and their relation 

 to it. 



Two out of the six poucJi -makers enumerated in the above list 

 are attacked, it is said, occasionally by one species of Psifliyrus, viz., 

 Ps. campestris^ which is not common. (I have not bred Ps. campestris 

 from any nest, it being rare in my neighbourhood, but I believe that 

 there are good grounds for stating that it does associate with B. 

 agrorum and, perhaps, also with B. Latreillellus). 



On the other hand, each of our two pronounced pollen-sforers, 

 B. lapidarius and terrestris, has a Psithyrus of its own, Ps. rupestris 

 and Ps. vestalis respectively, and both of these are common — in some 

 years abundant. B. terrestris is sometimes rendered quite uncommon 

 in a district by the attacks of its inquiline, Ps. vestalis. It is neces- 

 sary to know the life-history of Psithyrus to understand this. 



The female Psithyrus, on finding a nest of its host in a suitable 

 stage of existence, stings the queen to death and makes the workers 

 raise its young, which consist of males and females only. The usual 

 and best time for the Psithyrus to attack a Bomhus nest is when a few 

 workers have already emerged, and before the eggs destined to develop 

 into perfect Bomhus males and females have been laid. The brood 

 then consists entirely of workers, which will continue to hatch and 

 strengthen the working force of the nest for about three weeks after 

 the queen-mother has been destroyed. A Psithyrus female that finds 

 a nest of its host in an earlier stage than this endeavours to avoid a 

 combat with the queen until this stage has been reached. Owing to 

 her extra hard integument, which acta as a protective coat of mail, 

 the Psithyrus has a great advantage over her adversary, and I have 

 never known a case in which the Bomhus queen has been the victor. 

 Thus, in a nest attacked by Psithyrus the workers raise males and 

 females of the Psithyrus in the place of those of their own species. 



The Bomhus queen has often also to defend herself against the 

 attacks of other females of her own species, especially when the nest 



