Color: Varies; dull-colored body with clear wings
Legs: 6
Shape: Elongated; oval
Size: 1/32 of an inch to a little over one inch
Antennae: Yes
Region: Found throughout the U.S.
Mayflies most likely get their common name from their typical emergence during the month of May, though they can emerge earlier or later depending on the species and environmental conditions. Despite their name, mayflies are not actually flies. They are aquatic insects and are an important food source for fish and reptiles. Their most distinguishing features are their two or three tails that are often longer than their bodies.
Nymphs feed on microscopic algae and organic matter in the water. Adults do not eat because they don’t have functioning mouthparts, but this isn’t an issue because mayflies only live as mature adults for a few days.
Mayflies are nuisance pests and cannot bite or sting. They are, however, very attracted to light, which can result in massive swarms around buildings at night and piles of dead flies below lights and windows in the morning. In areas that see large swarms, mayflies could affect driving conditions and visibility. For allergy sufferers, mayflies could be a source of seasonal allergies. When they die, their molted skin and bodies break up and are easily carried by the wind.
As a primarily aquatic species, mayflies spend most of their lives developing in the water. They are common around freshwater sources such as streams, lakes or ponds. Adults leave the water to mate, and females will lay their eggs while flying low over the water or in the water directly. Mayflies are often seen as a sign of healthy water ecosystems because they are very sensitive to pollutants.
While there is little that can be done to prevent mayflies altogether, there are steps that can be taken to minimize the severity of the numbers around the home. White incandescent and fluorescent bulbs should be replaced with yellow bulbs. Homeowners should also ensure all screens are intact, and seal holes and cracks that might permit entry.
Adult mayflies don't eat at all. Mayflies have no functional mouthparts and survive on energy stored from their aquatic larval stage. As nymphs living underwater, mayflies feed on algae, organic debris, and tiny plant matter. Their brief adult life, often lasting just 24 hours, is focused entirely on mating and reproduction rather than feeding.
Mayflies typically hatch in late spring through early summer, with peak emergence occurring from May through June in most regions. The exact timing depends on water temperature and local climate conditions. Hatching usually happens in the evening or at night, when large swarms of adults emerge from the water simultaneously.
Mayflies are strongly attracted to light sources near bodies of water, which is why they often swarm around streetlights, porch lights, and illuminated buildings during their brief adult stage.