Niche width and inter-individual diet variation in predator populations are known to be affected by intrinsic factors such as body size, age, cognitive constraints, and by intra- and interspecific competition. By contrast, how variation in prey biological traits may affect niche width and partitioning is still a poorly explored topic. One of these candidate traits is prey mobility, which can affect the predators’ niche because acting on the rate of encounter and, assuming mobility as a proxy for escape capability, on the success of predator attacks. Here we analysed 20 wasp populations and their prey as individual-based food-webs to test if prey mobility may explain niche width (here defined by the Shannon entropy-based index Symbol) and patterns of inter-individual diet variation (here defined by the interaction-exclusiveness index H2′ and the interaction evenness index E2). Niche width was very variable among populations and overall network specialization (H2′) was always higher than the expected by null models. In case of high-speed flying prey (e.g. flies, bees), wasps showed wider niches (Symbol) and lower specialization (H2′) than in case of non-flying or slow-flying prey (e.g. spiders, beetles). Evenness (E2), on the other side, did not vary with prey mobility. Altogether, these results suggest that highly elusive prey may lead to wider predators’ niche but somehow limit their individual niche specialization.