Climatic conditions are widely thought to govern the distribution and abundance of ectoparasites, such as the blacklegged tick (Ixodes scapularis), vector of the agents of Lyme disease and other emerging human pathogens. However, translating physiological tolerances to distributional limits or mortality is challenging. Ticks may be able to avoid or tolerate unsuitable conditions, and what is lethal to one life history stage may not extend to others. Thus, even after decades of research there are...