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Which body features are most reliable for identifying adult mayfly species?

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A mayfly (Ephemera vulgata) with delicate, veined wings and long tail filaments clings to a green blade of grass against a blurred green background. — mayfly An adult mayfly (*Ephemera vulgata*) in Europe.

For the identification of adult mayfly species, the most reliable features are the characteristics of the male genitalia.1

While other physical traits—such as the patterns of veins in the wings—are useful for determining higher taxonomic categories like genus, they are not the primary diagnostic tools for identifying specific species.1