The transition of arthropods from an aquatic to a terrestrial lifestyle and then into the air imposed new challenges for their chemosensory systems. The nature of the early OR-based sensing systems in basal-winged insects remains unclear, with groups such as mayflies being largely overlooked for study. Next-generation sequencing techniques, antennal ultrastructure analysis, and molecular & functional characterization were undertaken to investigate the role of olfaction in NZ endemic mayfly, Coloburiscus humeralis. Overall, results suggest that this mayfly uses olfaction across its three different life stages.