NOTES ON PSITHYRUS. 29 



larval stage, then these small Psithyrus females are comparable to 

 Bremus workers. Whether or not they are more inclined to work 

 than the full-sized Psithyrus females remains to be determined. 



Sladen ('12, pp. 62, 63) believes that the Psithyrus queen, like 

 a dog, is largely guided by scent in locating the nests of her victims, 

 and is much more likely to find them when they have a short 

 tunnel. In support of this view, he points out that most of the 

 nests containing Psithyri which he dug up had tunnels not exceed- 

 ing fifteen inches in length, and that in no case were they more than 

 two feet long, and he thinks it is probable that species like Bremus 

 tcrrcstris Linnaeus and Bremus lapidarius often have longer tun- 

 nels than other species in order to escape the Psithyrus. That this 

 precaution is no absolute insurance against the invasion of Psithy- 

 rus ashtoni is indicated by the affinis-ashtoni nest with a tunnel of 

 more than seven feet. 



In a recent paper Frison ('19), on the basis of geographical dis- 

 tribution, expressed the belief that Ps. laboriosus " is an inquiline 

 in the nests of B. fervidus or B. vagans." The writer is pleased 

 to be able to confirm the last part of this prediction. On August 

 2, colony No. n (B. vagans} was dug up and transferred to a 

 third-story window in one of the Bussey buildings. Eight days 

 later (August 10) the writer found that a Ps. laboriosus queen had 

 gained admittance to the nest. At this time the vagans colony con- 

 sisted of the old queen, about 50 workers, and several males. In 

 the afternoon of the same day the Psithyrus queen was observed 

 in the act of tearing open a mass of wax containing small Bremus 

 larvae, so that three of the latter rolled to the bottom of the nest 

 box, leaving the remaining four widely exposed. As usual, these 

 larvae were thrown out of the nest a few minutes later by the 

 Bremus workers. About 5 P.M. the Psithyrus queen began to 

 gather wax from the cocoons and built a small cell in which, about 

 7 P.M., she laid several eggs. As each egg was deposited the sting 

 of the Psithyrus penetrated the wall of the cell. 



Hoffer ('88), who, despite his extensive observations, never saw 

 a Psithyrus oviposit, states (p. 100) that the Psithyrus queen lays 

 her eggs in pollen masses in which Bremus eggs, or larvae, are 

 already present. This, as is shown by the observations of Sladen 

 ('12) and of the writer, is not true of Ps. rupestris and Ps. lab on- 



