34 O. E. PLATH. 



released. Such a Psithyrus in turn was sometimes killed a few 

 minutes later by a third Psithyrus which was placed in the nest. 



The behavior of the Psithyrus laboriosus queens toward the 

 biuiaculahts workers differed essentially from that described for 

 the Ps. laboriosus queen in the vagans colony. Every one of the 

 1 6 laboriosus queens used in these experiments completely ignored 

 the bimaculatus queens and workers. Only once (shortly after she 

 had been introduced into the nest) was one of these laboriosus 

 queens observed raising one of her middle legs threateningly to- 

 ward a bimaculatus worker, a form of intimidation which is quite 

 frequent, even between members of the same Brcmus colony. 



Psithyrus laboriosus and Psithyrus ashtoni queens were also fre- 

 quently placed in two strong colonies of Brcmus iuipaticns Cresson, 

 one having about 125 workers and the other more than 450. As 

 soon as a Psithyrus queen was introduced into one of these nests, 

 a great uproar arose in the colony. The workers rushed madly in 

 every direction hunting for the source of the disturbance. The 

 Psithyrus queen was seized almost immediately by numerous work- 

 ers who tried to sting her, and was thus made absolutely helpless. 

 A few bellicose workers, unable to get hold of the Psithyrus, seized 

 some of the attached workers instead, and then attempted to sting 

 toward the center of the struggling mass. During one of these 

 experiments (August 15) such a fighting mass was lifted out of 

 the nest box with a pair of forceps. When the workers finally 

 released their hold, it was found that the mass had consisted of 17 

 workers and the Psithyrus. The latter and four of the workers 

 were mortally stung. Although the Psithyrus made attempts at 

 stinging during this struggle, one of the four workers was stung to 

 death by one of its fellows at the periphery of the mass, and it is 

 probable that the other three met death in the same manner. At 

 the beginning of two of these experiments two workers, in their 

 excitement, attacked each other (several inches from the Psithy- 

 rus') and one was stung to death. All of these experiments with 

 the B. impati'cns colonies always ended with the death of the 

 Psithyrus. 1 



i Prison ('21) reports that he found two Ps. laboriosus queens, one dead 

 and one paralyzed, in the nests of Bremus auricomas Robertson and B. penn- 

 sylvanicus, and expresses the belief that both were stung to death by the 



