Mayflies do not bite or sting nor feed on homes, furnishings, food, etc. The chief importance lies in their value as food for fish, dragonfly nymphs and birds. Antennae are short inconspicuous bristles. The head is large with round prominent eyes. Forelegs are quite long and stout.
Mouthparts are non-feeding.
Front wings are large, triangular, membranous with numerous longitudinal veins and cross veins. Wings are held upright and together over the body when at rest. After mayflies began to recolonize the Western Basin since 1991, their annual average densities in the sediment have increased dramatically. Hexagenia nymphs molt 20 to 30 times. There are three slender plumose tails on the body end.