Abstract <p>Although fleas (Siphonaptera) are a diverse group of insects with many species suspected of being threatened with extinction, their conservation needs are often overlooked. The Hercules flea (<i>Macropsylla hercules</i>) belongs to the evolutionarily distinct, basal, Australian flea family Macrospyllidae, sister to all other fleas. However, despite its large size and polyxenic host preferences, its distribution is not well resolved. This study sought to model the distribution of <i>M. hercules</i> to better clarify its range within Australia. We show that <i>M. hercules</i> is mainly isolated to Southeastern Australia within areas of high rainfall and moderate temperatures. Additionally, changes in habitat availability under future climate change scenarios were modelled to assess how global warming may impact this species. The results of this modelling suggest that future warming will likely result in major contraction in the available habitat for <i>M. hercules</i> with approximately 24%–48% of suitable habitat projected to be lost by 2100, depending on the emissions scenario.</p> Implications for insect conservation <p>Our results suggest that the availability of suitable habitat for <i>Macropsylla hercules</i> will contract under future climate change; with the more extreme warming scenarios associated with larger contractions in suitable habitat. This necessitates conservation planning to safeguard this distinctive flea species.</p>