Batesian mimicry is classically studied under the premise that aversion to noxious or dangerous animals is learned and is extended to the mimics, benefiting the mimics through reduced predation. We extend this model to include innate aversion to dangerous models (ants) and their mimics (jumping spiders in the genus Myrmarachne). We show that mantises with no prior experience with ants, or spiders, are averse to both ants and Myrmarachne, but not to ‘ordinary’ jumping spiders. We show that specialist spider-eating spiders are also averse to Myrmarachne, but that specialist ant-eating spiders are attracted to Myrmarachne, thus providing a rare empirical example of the costs associated with mimicry. Furthermore, Myrmarachne are sexually dimorphic. Although adult females and juveniles of both sexes are distinctly ant-like in appearance, Myrmarachne males have elongated chelicerae that might appear to detract from their resemblance to ants. Experimental findings suggest that the Myrmarachne male’s solution is to adopt compound mimicry; the male’s model seems to be not simply an ant worker but a combination of an ant and something carried in the ant’s mandibles. By becoming a mimic of a particular subset of worker ants, Myrmarachne males appear to have retained their Batesian-mimicry defence against ant-averse predators, but at the price of receiving the unwanted attention of ant-specialist predators for which encumbered ants are preferred prey.