The Ancient Mayfly Briefly Lives Only to Reproduce and Die 

Mayflies are flying insects in the order Ephemeroptera — the name "mayfly" translates to "short-lived with wings" in Greek. However, no matter how brief their lives may appear, like an iceberg, most of their lifespan happens under the surface of the water. Mayflies are common in almost any standing or running body of fresh water, where most of their lives are spent as larvae, growing bigger, shedding their skin over and over as they grow. A lot of species live in their larval stages for over a year — about as long as your average house mouse, which isn't a heroically long time by human standards, but it's more than just the few hours mayflies are generally given credit for.

That said, adult mayflies have only one job: to mate. They don't even have mouth parts because they don't take to the air to eat. The adults of some species live as few as two hours, which doesn't give them very much time to do all their reproduction business, but such is life for a mayfly.

"The winged stages of a mayfly's life are all about reproduction," says Luke Jacobus, a biology professor in the division of science at Indiana University — Purdue University Columbus, in an email interview. "The females lay eggs directly on or in the water, so they don't need to build burrows or nests. With only one thing to do, you don't need to live very long to get it done."

"Mayflies are the oldest living group of winged insects, dating back to the Carboniferous Period, about 300 million years ago," says Jacobus. "They have evolved to be specially adapted for life in water during their nymphal stages, and to be specially adapted for rapid and efficient reproduction."

Like a lot of other insects, mayflies cycle through different metamorphic stages during their lives — think of them as insect costume changes. The first two take place in the water as an egg and then a larva. After hatching, a mayfly larva feeds, grows and develops, some males building burrows to live in and feed from, while others just cruise around in the aquatic vegetation, finding snacks. During this time, they grow and molt over and over — as many as 50 times for some species.

Because they're such an old group of insects, they do things a little differently than the new-fangled insects you see these days. What's unique about mayflies is that, of their four life stages — egg, larva, subimago and imago, or adult — two of them have wings. This is unusual — a bit like Clark Kent going into his phone booth already wearing his spandex number with the cape and changing into another Superman costume.

"Mayflies are the only group of insects with two winged stages as part of their life cycle: the subimago and imago stages," says Jacobus. "The subimago is usually the stage that leaves the water, and the imago is usually the stage that reproduces."

So, if you time it right in the spring or fall, you can go down to the riverside at dawn or dusk and see quite a spectacle: thousands of seemingly adult mayflies crashing to the ground and writhing out of their winged skins to unveil yet another winged body that will only live a couple of days, on average.

Because time is of the essence during the adult life stage, some mayflies don't even need to mate to reproduce — females can produce viable female offspring through a process called parthenogenesis, a form of reproduction in which an egg can develop into an embryo without being fertilized by a sperm.

In some places, during some times of the year, mayflies can seem overwhelming to people — their sheer numbers can make it difficult to go outside sometimes. Gigantic swarms of them show up on weather radar during mass emergences from large lakes and big rivers.

However, unless you manage to accidentally inhale a mayfly and choke on it, they will not hurt you. In fact, in many cultures, mayflies are used as human food, and they have one of the highest protein contents of any edible insect. Their bodies even produce a molecule called low molecular weight chitosan, which has a lot of potential as an antitumor medicine.

Indeed, mayflies are an important part of the food chain in rivers, streams, ponds and lakes. Certain fish populations would be severely impacted if all mayfly species suddenly disappeared.

So, respect the mayfly — they are ancient, harmless, possibly helpful and you've got to hand to any creature that shows up on Doppler radar.