This study describes the nesting biology of the Egyptian cleptoparasitic wasp Sapyga luteomaculata Pic, which attacks the nests of two species of bees, Osmia submicans Morawitz and Megachile minutissima Radoszkowski, both belonging to the Megachilidae. We include descriptions of the egg/mature oocyte and of the first and last larval instars. We also identify the anatomical changes in the larva that take place as it transforms through intermediate instars from a host-killing first instar to a form adapted to feeding on the stored provisions supplied by the host. Biological subjects treated are egg deposition, ovariole statistics, eclosion, larval behavior including cocoon construction and defecation, and competition with other cleptoparasites. Comparisons are made throughout with accounts of other Sapyginae. Many biological and larval anatomical similarities between Sapyga and cleptoparasitic bees are recognized, and only a few possible cleptoparasitic novelties are identified.