We live on a microbial planet. Microorganisms dominate in terms of numbers of lineages, numbers of organisms, biomass and evolutionary innovations. Yet much remains to be learned about our microbial neighbours. We have gotten to know a few species that have been transformed into ‘laboratory rats’ (i.e. model organisms), but even here our understanding of the natural history of these lineages remains inadequate as there are few data from populations living in natural habitats. Zufall et al. (2013) move beyond this trend by providing insights into the natural history of Tetrahymena thermophila, a ciliate that has been used in many studies of cellular and molecular biology. Characterization of T. thermophila sampled from numerous ponds across this ciliate's range in Eastern North America reveals the following: (i) considerable differentiation among isolates, with the greatest diversity among lineages in New England, and (ii) a relatively small effective population size for this model ciliate. Such population data are fundamental for inferences about the origins of the numerous remarkable features of T. thermophila.