42 O. E. PLATH. 



out, it is but a step to the permanent social parasitism of the mem- 

 bers of the genus PsitJiyrus. 2 



This step in the probable evolution of the permanent social para- 

 sitism of PsitJiyrus is found among the ants. As Wheeler ('04, 

 '10, '19) was the first one to point out, there is a large group of 

 ants e.g.j Formica consocians in which the queens are no longer 

 able to found colonies of their own without becoming temporary 

 social parasites on other ants, a form of parasitism which is inter- 

 mediate between that of Bremus tcrrcstris and PsitJiyrus. 



SUMMARY AND CONCLUSIONS. 



i. The American PsitJiyri, whose habits have been studied, 

 rarely, if ever, kill the host queen. 



2. A PsitJiyrus laboriosus queen which is searching for bumble- 

 bee nests never tolerates another such Ps. laboriosus queen in the 

 same Bremus nest. 



3. During the first few days after a PsitJiyrus laboriosus queen 

 has gained admittance to a nest of her host, Bremus vagans, the 

 laboriosus queen intimidates the workers of the colony by rough 

 treatment. After this period of "getting acquainted," the mem- 

 bers of the vagans-laboriosns colony show no more hostility toward 

 each other than the members of an uninfested vagans colony. 



4. The PsitJiyrus laboriosus queen does not always, if ever, lay 

 her eggs in a pollen mass in which Bremus eggs, or larvae, are 

 present, but, like the Bremus queen, constructs her own egg-cells 

 and, like the latter, attaches them to one or more cocoons. 



5. In PsitJiynts-mfested nests of Bremus affinis and Bremus 

 vagans the destruction of the eggs, or young larvae, of the host is 

 probably caused by the PsitJiyrus, and not by her offspring. 



6. It is not necessary for the PsitJiyrus ashtoni queen, and prob- 

 ably also not for other PsitJiyrus queens, to forage for her offspring 

 in order that the latter may thrive. 



7. The representatives of the genus PsitJiyrus have probably 

 originated from several species of Bremus rather than from a 

 single one. 



8. Similarity in coloration between PsitJiyrus and Bremus spe- 



- Wheeler ('10, p. 451) considers it probable that the permanently para- 

 sitic ants went through a similar evolution. 



