In an attempt to determine whether Coelioxys and Radoszkowskiana, both cleptoparasitic members of the Megachilini, had a common cleptoparasitic ancestor, an investigation of the nesting biology and immature stages of C. (Allocoelioxys) coturnix Pérez was undertaken in Egypt. The purpose was to compare these aspects of this species with the results of a recent study of R. rufiventris (Spinola) and certain other species of Coelioxys (Rozen and Kamel, 2007). The egg of C. coturnix is deposited on the egg of Megachile minutissima Radoszkowski after the host female departs to collect cell-closure material. On hatching, the first instar, still surrounded by egg chorion, bites the developing host egg and consumes the entire egg content before feeding upon the host provisions. This behavior contrasts with certain other species of Coelioxys, whose eggs are hidden in the host cell while it is being provisioned and third instars normally kill the young host larvae. Because the behavior of C. coturnix closely mirrors that of R. rufiventris, the authors conclude that two modes of cleptoparasitism have developed in Coelioxys and that Coelioxys and Radoszkowskiana possibly had a common cleptoparasitic ancestor. The five larval instars of C. coturnix are described and compared with those of other Coelioxys species, and its first instar is compared with that of R. rufiventris.