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. Mercury-vapor lamps should be replaced with high-pressure sodium vapor lamps and 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.