Parasites are known to have direct effects on host dispersal ability and motivation. Yet, parasites have a variety of impacts on host populations, including shaping predation and cannibalism rates, and therefore may also have indirect effects on host dispersal; these indirect pathways have not been studied. We tested the hypothesis that parasites influence host dispersal through effects on cannibalism using backswimmers (Notonecta undulata) and Hydrachnidia freshwater mites. Mite parasitism impedes swimming in backswimmers, which we found increased their vulnerability to cannibalism. We imposed a manipulation that varied cannibalism rates across experimental populations consisting of a mix of backswimmers with and without simulated parasites. Using simulated parasites allowed us to examine the effects of cannibalism without introducing infection risk. We found that the odds of dispersal for infected backswimmers increased by 2.25× with every 10% increase in the risk of being cannibalized, and the odds of dispersal for healthy backswimmers increased by 2.34× for every additional infected backswimmer they consumed. Our results suggest that cannibalism was used as an energy source for dispersal for healthy individuals, while the risk of being eaten motivated dispersal in infected individuals. These results elucidate the complex ways that parasites impact host populations and strengthen our understanding of host-parasite interactions, including host and parasite population stability and spread. This article is part of the theme issue \'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics\'.

Dispersal determines the spatial dynamics of host-parasite assemblages, particularly during invasions and disease epidemics. The risk of parasitism may create an incentive for dispersal, but infection is expected to reduce dispersal ability, which may alter the host\'s dispersal response to biotic stressors, including population density. We measured the dispersal of a semiaquatic insect (Notonecta undulata) in aquatic mesocosms in which we manipulated the presence of ectoparasitic Hydrachnidia mites and infected conspecifics. We found that parasitism risk increases host dispersal propensity. Using a flight assay, we determined that parasite infection reduces host dispersal ability. Finally, we used a mark-release-recapture study to investigate the joint effects of both parasitism risk and parasite infection on host dispersal in a natural, spatially structured population. We found that parasitism risk reduced dispersal probability, eliminated positive density-dependent dispersal, and increased dispersal distance. Infection had no effect on dispersal in the natural population. Our results show that parasites can both increase and decrease the movement rates of their hosts, depending on the ecological context, and can alter the host\'s dispersal response to other biotic stressors. Future studies should consider the consequences of this double-headed impact of parasites for landscape connectivity, population persistence, and host-parasite coevolution.