NOTES ON PSITHYRUS. 33 



one another, because he never found a dead Psithyrus in a nest 

 ruled by a Psithyrus. This certainly is not true of Ps. laboriosus. 

 During June, July, and early August, Ps. laboriosus queens were 

 very common in the vicinity of Boston, so that numerous experi- 

 ments along this line could be carried out. The writer repeatedly 

 caught laboriosus queens which were searching for Brcmus nests 

 and placed them in a small box containing comb filled with honey. 

 Whenever two such queens were placed in this box, or in similar 

 receptacles without comb, they immediately engaged in a violent 

 battle which invariably resulted in the death of one of the com- 

 batants. 



Psithyrus laboriosus queens also repeatedly appeared in several 

 colonies of Breinus fervidus Fabricius and two of B remits bimacu- 

 latus Cresson, one consisting of the old queen and about 25 work- 

 ers, and the other of the old queen, several young queens, and 

 about 50 workers. All of these colonies were kept on the third 

 floor of one of the Bussey buildings. The fervid us colonies al- 

 ways expelled these intruders by a unique and very effective 

 method, which will be described in another paper. The two bi- 

 maculatus colonies, on the other hand, never seriously objected to 

 these intruders, and the latter sometimes stayed in their nests for 

 several days. However, neither of the b'nnacnlatus colonies pro- 

 duced any young Psithyri. 



Psithyrus laboriosiis queens which were searching for bumble- 

 bee nests were also frequently placed in these bimaculatus colonies. 

 If a laboriosus queen was already present in the nest, and another 

 one was introduced, the two Psithynts queens usually clenched 

 immediately, and within a minute or two, sometimes within a few 

 seconds, one toppled over, mortally stung. In one or two cases the 

 introduced PsitJiyrus queen tried to avoid a conflict by making a 

 dash for the flight-hole as soon as she noticed the other Psithyrus. 

 The two opponents, as a rule, seized each other by one of the legs 

 and endeavored to sting one another. As soon as one had suc- 

 ceeded in penetrating the body of her adversary with her sting, she 

 attempted to extricate herself from the embrace of her vanquished 

 foe. During these encounters it sometimes happened that legs 

 were torn off, or that the dead PsitJiyrus held firmly to one of the 

 legs of the victor with her mandibles so that the latter had to be 



