What to Know About Mayflies

Medically Reviewed by Dany Paul Baby, MD on April 20, 2022
5 min read

Mayflies are not exactly flies, but they have one of the most amazing lifecycles. There are more than 3,000 species of mayflies recognized globally. The only place that mayflies seem not to have colonized is Antarctica, although there are a few populations scattered across Greenland and Iceland. These insects have been around for more than 300 million years and are renowned by ecologists as major contributors to many ecosystems.

Mayflies are the only insects known to have two adult molts. They get their name from their typical emergence during the month of May. But they can come out earlier or later depending on the species and environmental factors.

These aquatic insects start their lives as eggs laid on the surface of water. The eggs sink to the bottom and hatch into aquatic nymphs, also called naiads, which then live around rocks and vegetation for months or years. They come up to the water’s surface to molt into a subadult and then, after a few hours, they molt again into reproductive adults. An adult mayfly lives for a few hours or days — just enough to reproduce — and then dies.

A mayfly is an aquatic insect that plays an important role in the ecosystem. They are a vital source of food for fish, frogs, toads, birds, and some reptiles. About 224 species depend on mayflies for nourishment.

Mayflies appear similar to dragonflies. They have hind wings that are smaller than the front wings, but their most recognizable feature is their two or three tails, which are known as styli. Adult mayflies do not feed because they don't have a functional mouth. 

Mayflies are important to fishing communities around the world. Some have hypothesized that they contributed to the origins of fly fishing. A lot of people use bait that resembles adult mayflies because fish can’t resist them.

They may be small in size and delicate in nature, but mayflies support the livelihoods of millions of people. Past studies have documented that mayflies are natural and rich sources of protein, minerals, B vitamins, and essential amino acids. They're also low in fat.

As many as 10 countries are known to have communities that directly feed on mayflies. For instance, in East Africa, the mayflies of Lake Victoria are collected from along the shoreline to be used as food. They're usually sun-dried and ground into flour that's used to make cakes and bread.

Mayflies are slender and elongated insects with two pairs of wings, six legs, and a set of antennae. Their styli are usually longer than their body. The size and color of a mayfly depend on the species. Some can be as small as 1-millimeter long while others can be up to 30-millimeters long. Most have dark, dull-colored bodies and yellow, gray, or even clear wings. Mayflies hold their wings together above their body when they're at rest.

Mayfly naiads may resemble the adults, but they don’t have wings. They have a characteristic appearance with a series of external gills attached either along their sides or on the top rear part of their abdomen. Their eyes are also smaller, and their heads are slightly flattened to allow them to hold on to rocks while they're in the water.

Mayflies are mostly found around freshwater bodies such as streams, lakes, or ponds. Most of their lifespan is spent developing in water. That’s why ecologists view them as an important sign that the environment they live in is healthy. Mayflies are particularly sensitive to pollutants and will thrive in clean, unpolluted water. 

Female mayflies need clean water to lay their eggs, which they do while flying low over the surface. Sometimes they'll deposit their eggs directly into the water. The life mission of a male mayfly is to mate, and a female’s mission is to lay eggs. Once they complete these goals, their lives come to an end. 

Most people know mayflies due to their incredible swarms. They often cause a feeding frenzy among fish, but they can be a nuisance when they swarm in residential areas or around streetlights.

Apart from causing a disturbance where they swarm, mayflies don’t bite or sting. They are particularly attracted to light, which can lead them to swarm around buildings at night. Due to their short lifespans, mayflies die in large numbers and pile up below lights and windows. When mayfly bodies dry up, they are easily carried off by the wind. This can cause allergic reactions in people sensitive to allergens.

Mayflies are known to congregate in such large numbers that their swarms affect visibility and even driving conditions. The swarms can grow up to 125–250 meters thick. Mayfly swarms can cover areas tens or hundreds of square kilometers in size.

Some mayfly species have legs and tusks modified for digging and burrowing. They can bore into wood and, as a result, cause problems to submerged human structures.

Mayflies simply thrive in nature, so very little can be done to get rid of them. But if they cause a disturbance around your home, the best thing to do is to change your lights. Because they're primarily attracted to white light, changing your bulbs to yellow ones can keep them away. 

To prevent mayflies from getting inside your house, add screens to your doors and windows and make sure they're secure. Also, make sure any holes and cracks are properly sealed. In most cases, you just have to let the mayflies be. But you could call a pest control specialist to help you get rid of them professionally. 

As small as they are, mayflies are one of the most important insects that live on earth. For hundreds of millions of years, these insects have transferred nutrients among themselves and many other organisms. They're vital for human survival and should be protected. Whenever possible, it's important to focus on helping them thrive where they belong by taking care of freshwater bodies and not using chemicals to try to control them.