Maculinea butterflies in Europe, and probably most of Asia, are host specific social parasites of various species of Myrmica ants. The latest summary of field data showing the pattern of host specificity by Maculinea is presented. Myrmica ants have been well studied in the laboratory but much less is known about the ecology of their natural populations. While the former is important in understanding the adaptive evolution of Maculinea larval behaviours, the latter is of more practical importance to conservationists charged with the protection of specific populations of Maculinea. The current knowledge of habitat partition, colony growth and colony reproduction within communities of Myrmica ants is summarized in relation to the ecology of Maculinea species. Concepts used in current population simulation models are explained. A key concept is the idea that community structure (both number of species and size and abundance of nests) is controlled by the quantity and quality of suitable nest sites. Some advice is given to conservationists who might need to manipulate Myrmica ant populations in order to maintain a robust population of a Maculinea species.