Mayflies (order Ephemeroptera) are aquatic insects known for their brief adult life stage. They are harmless, as they do not bite, sting, or possess functional mouthparts. However, their synchronized emergence from water bodies near homes creates massive swarms that become a nuisance, blanketing structures and outdoor areas. This phenomenon, often called a “hatch,” drives the need for effective methods to deter them from congregating.
Understanding Mayfly Attraction
The primary factors drawing adult mayflies are their proximity to the aquatic environment where they develop and their sensitivity to light. Mayflies spend most of their lives as nymphs underwater, sometimes for up to a year, before emerging to reproduce. Once emerged, adults have a short lifespan, often lasting only 24 to 48 hours, with their sole purpose being to mate and lay eggs.
The second, more controllable factor is their strong attraction to light, known as phototaxis. This behavior is pronounced because mayflies often swarm around dusk and dawn, and artificial lights mimic the open sky they use for navigation. Disrupting this attraction is the most effective way to keep swarms at bay during the emergence season. Their attraction is highest for short-wavelength colors, such as ultraviolet (UV) and blue light, which informs deterrence strategies.
Modifying Exterior Lighting
Changing the light sources on a property is the most effective strategy for reducing mayfly swarms. Mayflies are sensitive to short-wavelength light (UV and blue), which is emitted by traditional incandescent, fluorescent, and some white LED bulbs. Switching to light sources that emit longer wavelengths makes homes less visible and appealing to the insects.
The best alternatives are yellow, amber, or sodium vapor lights, as these colors fall outside the most sensitive part of the mayfly’s visual spectrum. Specifically, “bug lights” or yellow LED bulbs are designed to emit light in the yellow-orange spectrum, which is significantly less attractive to most night-flying insects. Replacing white porch lights, security floodlights, and landscape lighting with these warm-colored alternatives can drastically cut down on congregating mayflies.
Beyond changing the color, reducing light intensity also plays a role in deterrence. The brighter the light, the greater the attraction, so using lower-wattage bulbs is an easy adjustment. Installing motion sensors means lights are only active when necessary, minimizing the window for attraction during peak emergence times. Turning off non-essential exterior lights entirely during the evening hours of the hatching season is the simplest method of light management.
Physical Barriers and Property Cleanliness
Implementing physical barriers helps prevent the insects that are still attracted to the area from entering the home. Mayflies are weak flyers, making it easier to exclude them from covered areas and open doorways. Ensuring that window and door screens are intact and use a fine mesh can block entry points, while sealing small gaps around window frames, vents, and doors with caulk or weather stripping is beneficial.
For high-traffic entry points, air curtains or high-velocity fans can be positioned to create an invisible barrier that disrupts the mayflies’ flight path. The sustained, powerful stream of air is difficult for the insects to penetrate, effectively redirecting them away from an entrance while the door is open. This non-chemical method creates a physical deterrent without relying on sprays, which are generally ineffective against the sheer volume of a mayfly swarm.
Managing the aftermath of a swarm is a necessary aspect of property maintenance. After adult mayflies complete their reproductive stage, they die in mass numbers, creating large piles of carcasses and shed skins. Rapid removal of these dead insects using a broom, leaf blower, or hose is important because the accumulated bodies create slick, hazardous conditions on walkways and can attract other scavenging insects.