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How large can North American mayflies grow?

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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.

In North America, adult mayflies vary significantly in size depending on the species. Their body length, excluding their tails, ranges from approximately 2.5 mm (0.1 inch) for the genus Caenis to 32 mm (more than an inch) for the genus Hexagenia.1