As a case study of how insects use masks as a defence against vision-guided predators, an experimental study was carried out using Acanthaspis petax, a reduviid bug (‘ant bug’) that covers itself with a ‘mask’, or ‘backpack’, made from carcasses of its preferred prey (ants), and three salticid spider species, Hyllus sp., Plexippus sp. and Thyene sp., salticids being predators with exceptionally acute vision. The ant bugs and the salticids were from the Lake Victoria region of East Africa. In each test, a salticid was presented with a live bug or a lure made from a dead bug, with the mask removed (‘naked’) or intact (‘masked’). Salticids made predatory responses to naked bugs significantly more often than to masked bugs. These findings suggest that salticids readily identify naked bugs as prey, but fail to identify masked bugs as prey.