Theory predicts that the direction of local adaptation depends on the relative migration rates of hosts and parasites. Here we measured relative migration rates and tested for local adaptation in the interaction between a tree hole mosquito (Ochlerotatus sierrensis) and a protozoan parasite (Lambornella clarki). We found strong support for the hypothesis that the host migrates more than its parasite. Hosts colonized artificial tree holes in the field at a much higher rate than the parasite. Field releases of the parasite demonstrated that it colonizes and persists in natural tree holes where it was previously absent, suggesting that parasite distribution is limited by its migratory ability. Although the host migrates more than its parasite, we found no evidence for local adaptation by hosts and some evidence for local adaptation by parasites. Other life history traits of the host and parasite may also influence patterns in local adaptation, particularly parasite virulence and host dormancy.