When do mayfly mass emergences usually occur?

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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.

Mayfly mass emergences typically occur during the summer months. These brief, annual events involve the emergence of winged adults in such vast numbers that they are often detectable on weather radar. During these swarms, the insects may create hazards by making roads slippery, clogging gutters, or producing an odor of decay.1