Herein is presented nesting information on the communal ground-nesting Argentinian bees Rhophitulus xenopalpus Ramos and R. mimus Ramos, which is compared with what is known concerning the closely related Brazilian bee Cephalurgus anomalus Moure and Lucas de Oliveira. The mature larvae of all three taxa are described, illustrated, and compared with one another and with those of other Protandrenini. While larvae of the three species share many similarities, those of R. xenopalpus and R. mimus, though each distinctive, are quite similar, and those of C. anomalus differ from the others in mandibular features and in dorsal body ornamentation. Male and female pupae of R. xenopalpus are also described.