Abstract – Thelytokous Apis mellifera capensis workers recently brought into regions occupied by the arrkenotokous African bee A. m. scutellata, parasitise these colonies, causing colony death. These capensis workers are genetically almost identical and are referred to as a ‘pseudo–clone’. We surveyed 120 scutellata colonies, 27 in detail, at various stages of usurpation by the pseudo-clone. The scutellata queen could co-exist with egg-laying pseudo-clones for 50+ days in one case but disappeared 1–15 days in three other cases. Despite the presence of emerged queen cells no new adult queens of either race were observed in usurped colonies. Only 11 ± 13 % of the pseudo-clone population had fully active ovaries, suggesting ovarian development is inhibited in the majority of the pseudo-clones. Only 2.7 ± 1.7 % of the foraging force were pseudo-clones. The data were modelled and showed the rapid (56–105 days) growth of the pseudo-clone population and colony death over a wide range of initial conditions.