All species from the jumping spider (Salticidae) genus Portia appear to be predators that specialize at preying on other spiders by invading webs and, through aggressive mimicry, gaining dynamic fine control over the resident spider’s behaviour. From previous research, there is evidence that P. fimbriata, P. labiata and P. schultzi derive signals by trial and error. Here we demonstrate that P. africana is another species that uses a trial and error, or generate-and-test, algorithm when deriving the aggressive-mimicry signals that will be appropriate in different predator-prey encounters. We discuss the implications of these new findings and the findings from previous work for understanding the selection factors that drive the evolution of flexibility in aggressive-mimicry strategies.