in PSITHYRUS, THE USURPER-BEE 71 



abdomens, 16 young barbutellus queens, 2 small 

 barbutellus males, and the body of the old barbutellus 

 queen. The brood consisted of 38 Psithyrus cocoons 

 containing pupae, chiefly queens, and a cluster of 5 

 kortorum cocoons containing younger pupae, all of 

 which developed into males, besides a few larvae and 

 eggs. Probably therefore Ps. ba?'b7itellus is parasitic 

 in the same deadly way as Ps. rupestris and vestalis. 



There is a greater or less tendency in all the 

 species of Psithyrus to resemble their particular 

 hosts in the pattern and colour of their coat. It can 

 hardly be doubted that this is of some advantage 

 to the Psithyrus. 



The origin of Psithyrus, more especially of its 

 peculiar parasitical instincts, is an interesting question. 

 If a specimen of Psithyrus be compared with a speci- 

 men of Bombus it is seen that the resemblance is 

 not merely superficial but extends to nearly all the 

 important details of structure, so that it is impossible 

 to avoid the conclusion that Psithyrus has sprung 

 from Bombus, and this at quite a recent period in the 

 history of life. Moreover, the Bombi and this is 

 particularly interesting show parasitical tendencies 

 leading to fhe parasitism of Psithyrus. We have 

 seen (pages 55-58) how the Bombus queens may 

 enter the nests of their own species and kill one 

 another, and how, in the case of the twin species, B. 

 terrestris and lucorum, terrestris has extended this 

 habit so as to prey on lucorum, killing the lucorum 

 queen and getting the lucorum workers to rear her 

 young in practically the same manner as the Psithym 



