When present in large numbers, they can be annoying. The larvae develop in water, such as lakes, ponds, streams, and pools. Mass hatching may occur and the spontaneous appearance of large numbers may cause concern. Their larvae also live in water and have a characteristic U-shape. Adults are slightly smaller than mosquitoes and are often found in swarms at dusk.
Adults live less than one week.
Adult mayflies live one to two days and do not feed. The adults molt once, leaving their old cast skin on the wall surface where it was shed. They are easily recognized by a triangular wing and two or three thread-like tails. Larvae are an important food for many freshwater fish. Eggs are laid on rocks or other objects in the water.