The theory of automimicry is explored mathematically on the assumption that predators can learn to avoid noxious prey by sight for some finite period after a single noxious experience. Automimetic advantage is an inevitable consequence of the evolution of an unpalatability dimorphism. An established automimetic situation is analogous to an established perfect Batesian mimicry situation, although the evolutionary bases of the two phenomena are different. In both situations, the mimetic advantage depends upon the proportion of unpalatable prey, the memory span of the predators, and the abundance of the prey relative to the predators. Automimetic advantage is maximal when the prey are neither too common nor too rare. Remarkably low proportions of unpalatable prey can confer very substantial immunity to the population. A surprising prediction of the model is that the evolution of unpalatability will not occur in rare prey species unless they first become Batesian mimics. This in turn could lead to the evolution of mimicry complexes containing many species forming a whole spectrum of unpalatability.