Herein we describe the mature oocyte and last larval instar of Stelis (Stelis) murina Pérez, a cleptoparasite associated with Osmia (Pyrosmia) submicans Morawitz near Ismailia, Egypt. The mature oocyte is compared with that of Stelis (Stelis) elongativentris Parker and found to be approximately equal in size. The mature oocyte of S. murina is also very close in size to that of its host, an unusual phenomenon in host-cleptoparasite relationships in bees.

A review and analysis based on literature accounts of what is known about the mode of cleptoparasitism of Stelis is offered. Added are observations on the biology of Stelis murina resulting from our fieldwork.

The mature larva of Stelis murina is described and found similar but not identical to those of other known Stelis larvae. We also include a preliminary key to the genera of cleptoparasitic megachilids based on known mature larvae and also a summary describing the modes of cleptoparasitism by these taxa.