Why have burrowing mayfly populations declined in some parts of the United States?

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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.

Burrowing mayfly populations (Hexagenia species) have experienced a decline of more than 50 percent in certain regions of the United States. This significant reduction is primarily attributed to three environmental factors that disrupt their aquatic nymphal stage:

Water pollution: Contamination of freshwater habitats negatively impacts the survival and development of the nymphs.
Insecticide use: The application of chemical pesticides can be toxic to these insects, leading to population losses.
Algal blooms: These events can alter the aquatic environment in ways that are detrimental to the nymphs' ability to thrive.

Because mayflies serve as essential members of local food webs and play a vital role in the energy transfer cycle of freshwater ecosystems, these declines have notable ecological implications.1