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eand D. australe, we studied the behaviour of new callows confronted with dominant individuals of differ-ent fertility or age. Faced with a young unmutilated worker (the future gamergate with poorly developed ovaries), callows were aggressive, whereas they did not resist gamergates. We interpret this dichotomy in terms of reproductive differentials between actors and victims. We discuss the selective advantages of mutilation relative to dominance hierarchies which other queenless ants use to regulate monogyny. Mutilation seems to maximize colony productivity by creating irreversibly sterile helpers from newly emerged individuals. 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Reproductive conflicts in ants are strongly influenced by the occurrence of two female castes. Queens and workers diverge irreversibly during larval development and workers generally cannot reproduce sexually. However, in about 200 species of queenless ants, colonies consist exclusively of workers with equivalent reproductive potentials (Peeters 1991; Peeters & Ito 2001). Aggressive interactions lead to hierarchies, and one or a few domi-nant workers mate and lay eggs (e.g. Ito & Higashi 1991; Monnin & Peeters 1999; Gobin et al. 2001; Cuvillier-Hot et al. 2004a). Importantly, subordinate individuals retain the ability to replace the ‘gamergate ’ (mated egg-laying worker). A qualitatively different type of behavioural regu-lation characterizes the genus Diacamma, because the gamergate systematically bites off the ‘gemmae’, a pair of tiny appendages filled with exocrine cells present on the thorax of all emerging workers (Fukumoto et al