Abstract. The stalking behaviour of four species of jumping spiders, Portia fimbriata, P. labiata, P. schultzi and P. africana, was examined to determine whether Portia opportunistically exploits situations in which the prey spider is distracted by environmental disturbances. Disturbances were created mainly by wind blowing on webs and a magnet shaking webs. All four Portia species moved significantly further during disturbance than during non-disturbance, a behaviour labelled 'opportunistic smokescreen behaviour'. Portia can discriminate between spiders and other prey such as live insects, wrapped-up insects in the web, and egg sacs, because Portia used opportunistic smokescreen behaviour only against spiders and not against these other types of prey. If the location of disturbances and the location of prey differ, Portia can accurately discriminate between them. Portia's smokescreen behaviour apparently is a true predatory tactic because Portia attacked prey more often during disturbances than at other times. Smokescreen behaviour appears to work in part because the disturbances that Portia uses for smokescreens interfere with the prey's ability to sense Portia's stalking movements.