Abstract The competitive interactions between Latrodectus katipo and Steatoda capensis were studied under the hypothesis that L. katipo is being displaced from its natural habitat by competition from S. capensis. Use of trophic and spatial resources were studied. High overlap for both resources was found. Data on reproductive potential revealed that S. capenisis has a significantly higher reproductive output. Laboratory predation experiments indicated L. katipo adults are not inferior to S. capensis. Evidence suggesting displacement following L. katipo population crashes was obtained. Differences in reproductive potential and seasonal reproduction are proposed as the mechanism underlying the displacement.