140 Psyche [Oct.-Dec. 



invaded by Psithyrus and to the queen of B. terrestris lucorum 

 when its nest is invaded by the queen of B. terrestris virginalis.' 

 Had the Colebrook arctica-diaholica colony, which was still young 

 when asphyxiated, been permitted to continue its gi'owth and 

 development, the diabolica queen might, of course, have been elim- 

 inated. This would, indeed, seem probable, if we may judge from 

 the observations of Eobson and Carpenter and Pack-Beresford on 

 austriaca-rufa colonies, which were well- developed when examined. 

 The colony observed by Eobson had no rufa queen, but must have 

 been founded by one, since typical rufa males were present. He 

 saw the rufa workers dragging out of the nest the decapitated and 

 mutilated carcass of an austriaca queen, presumably after her brood 

 had been reared by the rufa workers. Thus it would seem that in 

 this colony the host-queen had been killed either by her own workers 

 or by the parasitic queen, and that the latter had been killed by 

 the rufa workers or had died a natural death in the nest after com- 

 pleting her life-work. Carpenter and Pack-Beresford give a de- 

 tailed census of their austriaca-rufa colony. It contained an old 

 austriaca but no rufa queen, besides many males and three pupal 

 queens of austriaca. In this case also, the host queen seems to have 

 been eliminated earlier in the season. 



The absence of the host-queen from nests infested by the para- 

 sitic wasps, as in the nests of austriaca-rufa just considered and 

 the two arctica-diaholica nests found by the junior author, may be 

 due, nevertheless, to quite other causes. Desertion of the nest by 

 its foundress, even after brood is present, or her destruction while 

 foraging, may leave the colony motherless and open to invasion 

 by parasitic queens. Janet (1903) has even observel the invasion 

 of a motherless V. crahro nest by a strange crabro queen, and her 

 adoption by the workers. Both Janet and Marchal (1896) have 

 failed to find the queen in several nests of this wasp, and the latter 

 shows that in the case of V. media the queen is so short-lived that 

 she completes oviposition by the beginning of August and dis- 

 appears soon afterwards. The development of media colonies is, 

 therefore, considerably accelerated as compared with the colonies 



' This rule does not seem to apply to some of our American Psithyrus- 

 Bom bus colonies, to judge from the very interesting, unpublished observa- 

 tions made by Mr. O. E. Plath at the Bussey Institution during the past 

 summer. 



