Rewilded horses as a nature-based solution for wintertime tick control in Japan: help or hindrance?

The control of ticks is challenging owing to their ubiquity, complex ecologies, and difficulties relating to costs and non-target impacts of chemical control programs. Nature-based solutions centre around co-opting natural processes and biodiversity to address socio-environmental problems; and in some cases, rewilded species can provide nature-based solutions. In northern Japan, the winter ecology of ticks is poorly studied, though some species are believed to overwinter under the snow. Winter grazing activity of rewilded horses may disturb overwintering ticks, exposing them to sub-zero temperatures and killing them, thereby providing a nature-based solution to tick control. In this study we sought to ascertain: (i) whether ticks in Japan overwinter in leaflitter under the snow, (ii) whether the winter grazing activity of semi-rewilded horses is associated with reduced springtime tick abundance, (iii) whether semi-rewilded horses serve as key hosts for ticks during springtime. Paired leaflitter sampling undertaken at 10 sites during autumn and winter, respectively, showed that Haemaphysalis ticks overwinter in leaflitter under the snow. Using six paired 25 m² exclusion-grazing plots we tested whether winter horse grazing was associated with reduced springtime tick abundances but found no significant relationships. Springtime surveys revealed extremely low tick loads (0.2 ticks per horse) and prevalences (12%) on semi-rewilded horses. This suggests that while the winter grazing activities of horses may not appreciably reduce tick abundances, that horses likely do not serve as important amplifying hosts of ticks in northern Japan and that rewilded horses are neither a help nor hinderance to local tick control efforts in this region.