Upper-mississippi-valley
Guides
Hexagenia bilineata
Emergent Mayfly
Hexagenia bilineata is a burrowing mayfly native to the Upper Mississippi Valley of North America. The aquatic nymphs construct U-shaped burrows in mud and silt, filtering organic detritus for food. Adults emerge synchronously in enormous numbers during summer evenings, creating spectacular swarms that have caused documented traffic hazards and infrastructure damage. The species exhibits mixed voltinism, with some populations completing development in one year while others require two years.