Germ cell segregation and gamete production are developmental problems that all sexually reproducing species must solve in order to survive. Many people are familiar with the complex social structures of some insect species, where specialised castes of adult insects perform specific tasks, one of which is usually to guard the sexually reproductive queen. The parasitic wasp Copidosoma floridanum adds another level of complexity to the caste system: a fertilised egg produces both sterile, short‐lived “soldier” larvae and “reproductive” larvae that complete (...) metamorphosis to produce sexually reproductive adults. How two morphologically and functionally distinct larval castes are produced by genetically identical groups of cells developing under the same environmental conditions is a baffling problem. A recent paper suggests that differential germ cell segregation during embryogenesis may be an event both necessary and sufficient for caste determination.1 BioEssays 26:1263–1267, 2004. © 2004 Wiley Periodicals, Inc. (shrink)