Massacre of the innocents in Cardiocondyla thoracica: Manipulation by adult ant males incites workers to kill their immature rivals

Wingless males of the ant genus Cardiocondyla exhibit a remarkable range of intrasexual competition, from mutual tolerance among males in the colonies of some species to regular lethal fighting in the nests of others. Here, we describe male–male antagonism in Cardiocondyla thoracica (Smith, 1859) from Northern Australia. Males appear to widely ignore adult competitors, but grab defenseless, young rivals during or immediately after emergence and daub them with hindgut secretion. This fluid elicits fatal worker aggression against the besmeared individual. Besmearing and subsequent worker aggression is known from other species of Cardiocondyla but is usually directed towards adult contenders, whereas males kill freshly eclosing males by biting or dismembering. The behavior of C. thoracica males thus constitutes a novel nuance of rival elimination.