Macroparasites are often aggregated across the host population, whereby a few individuals are heavily infected while most have no or few parasites. Many processes may contribute to this pattern of aggregation. Most often host ecology and physiology are cited as important factors. Few studies have considered the role that parasites play in generating aggregation, for instance by actively choosing to infect certain types of hosts. Emily is investigating whether mites show active preference for hosts that are already infected. If so, this may be an important mechanism driving the aggregation of parasites in natural host populations.