Mayflies

In the predawn light, through the glass of my 7th-floor apartment window, I saw the underside of a delicate mayfly. I tried to get a photograph, but the combination of glass, lighting, and reflection made my attempts unsuccessful. This was unfortunate because mayflies are quite lovely. And, while they do not have a direct impact on your garden, their presence says a lot about the health of an ecosystem.

Female subimago mayfly (Richard Bartz) CC BY-SA 2.5

Mayfly description

Prehistoric mayflies had 18-inch wingspans. They are significantly smaller than that these days. My morning visitor was less than an inch long, tail included. Mayflies are members of the Ephemeroptera order, which includes dragonflies and damselflies. There are over 3,000 species of mayfly around the world and 630 in North America, though four North American species have become extinct. Mayflies are also known as fishflies and shadflies. Fly fishermen from around the world have used these long-tailed insects as models for lures.


Those long tails are often split into two fine hairs, much like the first flying insects. When at rest, as was my morning visitor, they hold their wings upright, similar to butterflies. Their relatively long wings are often mottled.


Life as a mayfly

Mayflies are aquatic insects. They spend most of their lives as nymphs, or naiads, in unpolluted freshwater. These naiads look something like a cross between an immature ladybug alligator and a leafhopper. Sort of. They may spend several years in this stage, molting through 10 to 50 instars. In some cases, they breathe using gills. Most species of mayfly get enough oxygen by absorbing it through their outer covering, or integument. Most mayfly nymphs feed on algae and debris, though a few are predators. In turn, most mayflies are eaten by fish and carnivorous insects. Eventually, surviving nymphs leave the water, and sometimes in astounding numbers. Contrary to their name, adult mayflies can appear spring through autumn and not just in May.


Mayfly lifecycle

Unlike most other insects, most mayfly species have an aerial pre-adult stage, called the subimago or dun. The subimago looks similar to an adult but is sexually immature. These teenage mayflies don’t fly very well, are a duller color, have shorter appendages, and they lack the sexy wing coloration of mature adults. Some subimagos have forelegs that are accordion-folded, which don’t extend until they reach adulthood. How’s that for a growth stage?

Mayfly nymph (Ian Alexander) CC BY-SA 4.0

The subimago stage lasts only a few minutes to a few days, depending on the species before they molt into sexually mature adults or imagos. This is where the ephemeral nature of the species becomes apparent. After swimming around for several years, adult mayflies have only one purpose, to mate, and they may have only minutes, hours, or days in which to succeed.


They do not have mouths because they do not have time to eat. Some male mayflies have eyes on top of their heads, in addition to the front-facing variety, to help them find females during their short lives.


Male mayflies dance in an up-and-down pattern to attract females. After copulation, many female mayflies fly upstream to lay between 400 and 3,000 eggs. Female mayflies find water by detecting reflected light. In some cases, this means they are fooled into laying their eggs on other shiny surfaces.


When laid in water, these eggs sink to the bottom where they may take a few days or up to a year to hatch. After hatching, first-stage nymphs burrow into the sediment where they feed for a few years.


Mayflies are very sensitive to pollutants, making them something of a canary in a coal mine. They are also intermediary hosts to horsehair worms, which infect grasshoppers, causing them to commit suicide by drowning. I cannot make this stuff up. Finally, mayflies contain the most raw protein of any edible insect, in case you get hungry.

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Have you seen mayflies in your garden? Are there any other insects you use as guides to your garden’s health? let us know in the comments!