Biodiversity ultimately depends on the origin of species by natural selection. Coevolution is thought to be especially important in increasing the diversity of species. One of the frequent outcomes of coevolution is that a single parasite species adapts to exploit several different hosts. Such differences in host use can be observed between individuals in a single population, which is vital when a (social) parasite population has to adapt to a new host species. Larvae of Maculinea butterflies are social parasites of Myrmica ant nests, and are probably already the best-studied social parasites, which makes them a good model for studying the coevolution between (social) parasites and their hosts. There are differences in their host ant specificity on the population level. I hypothesise that the individual differences within the multiple-host ant using Maculinea populations should be greater than within single-host ant using ones, based on the different mechanisms and strategies required to successfully infect the different hosts. I also hypothesise that peripheral populations are less genetically variable, and potentially less able to adapt to new host ants. Specialization on a single host species is expected to lead to a reduction in behavioural repertoire and diversity of surface recognition compounds. To examine this pattern, individual-level differences of Maculinea alcon larvae will be compared in multiple- and single-host populations, combining analysis of genetics, behaviour and cuticular compounds. The results of this study will not only provide insights into the importance of individual differences, but will be directly relevant for the conservation of endangered Maculinea butterflies in Europe. This project will give me new experience of the analysis of chemical recognition cues and genetics, and will involve collaboration with local researchers across Europe. Together, this will benefit my future independent research career.