68 THE HUMBLE-BEE 



in 



observations are opposed to those of H offer, who 

 found the Psithyms queen and the Bombus queen 

 living in the nest on good terms with one another, 

 and both of them producing young males and queens. 

 But H offer's observations were made chiefly on two 

 species of Psithyms which I have not been able to 

 study, namely, Ps. campestris, which breeds in the 

 nests of B. agrorum and B. helferanus, and Ps. 

 quadricolor, which preys on B. pratorum. Evidently 

 these species of Bo?)ibus, which, it may be noted, are 

 milder tempered than B. lapidarius and terrestris, do 

 not object, in Styria at least, to the Psithyri laying 

 their eggs in their nests. Of course, the Psithyri, 

 in these cases, do not rear so large a family. 



I believe the Psithyms queens do not kill one 

 another, for I have never found a dead Psithyms in 

 a nest ruled by a Psithyms. If several Psithyri find 

 the same nest only one remains, although the others 

 may make it their headquarters for a few days, as 

 noticed in the above-mentioned nest of B. lapi- 

 darius. 



As might be supposed, the Psithyms is at first 

 very prolific, but she ages and fails more quickly 

 than a Bombus queen. 



The eggs of Ps. rupestris are slightly longer, but 

 much more slender, than those of B. lapidarius, 

 being four times as long as they are thick : the eggs 

 of Ps. vestalis are also slenderer than those of 

 B. terrestris. 



The development of Psithyms through the larval 

 and pupal stages is the same as that of Bombus, but 



