While they are considered annoying pests, mayflies do not bite or sting. Their presence is actually an indicator of a healthy aquatic environment, as they are a chief food source of birds, dragonfly nymphs and fish.
Abundant near creeks and bodies of water all over the United States, mayflies form massive swarms in late June through early July, often accumulating around lights and on the walls of buildings. Surviving just several hours to a few days, they are one of the shortest-living species of the insect in the world. For some, the dead, fragmented bodies of the insects trigger hay fever and asthma, while mass accumulations create an offensive, fish-like smell.