#ephemeroptera

Mayflies were some of the first animals to develop flight, and retain ancestral traits that were most likely present in the first flying insects, such as long tails and wings that do not fold flat over the abdomen.

Mayflies spend most of the life in their immature stage: as aquatic, freshwater larvae called “naiads” or “nymphs”. The presence and concentration of mayfly nymphs in a body of water are used to indicate whether the environment is clean, unpolluted and highly oxygenated, as they do not thrive in polluted environments.

Mayflies are highly unique among insect orders in having a fully winged terrestrial preadult stage, the subimago, which moults into the reproductive form, the imago. The subimago stage does not last for long, rarely for more than 24 hours. In some species, it may last for just a few minutes, while the mayflies in the family Palingeniidae have sexually mature subimagos and no true adult form at all. Nevertheless, no other insect has two flighted adult forms.

Mayflies molt into their adult forms from spring to autumn (not necessarily in May) in enormous numbers. Often, all the individuals in a population will emerge from the water at the same time. In many species the emergence is synchronised with dawn or dusk, and light intensity seems to be an important cue for emergence, but other factors may also be involved. These emergences do not last long, as the mayfly’s final form only exists long enough to reproduce; they do not feed and have only vestigial mouthparts, while their digestive systems are filled with air, surviving only off the energy gathered from their time as a nymph. Males dance to attract as many females as possible, and mating takes place in the air. Females lay their eggs in the water, and die shortly after.

The emergence of the Giant Mayfly, or Tisza Mayfly, (Palingenia longicauda) on the Tisza River in Hungary and Serbia, known as "Tisza blooming", is a tourist attraction. The species is now extinct in many European countries, so this river is one of the last places to see the emergence of the largest mayfly species in Europe.

The 2014 emergence of the large Emergent Mayfly (Hexagenia bilineata) on the Mississippi River in the US was imaged on weather radar. The swarm flew up to 760 m (2,500 feet) above the ground near La Crosse, Wisconsin, creating a radar signature that resembled a "significant rain storm", and the ensuing mass of dead insects covered roads, cars, and buildings in a "slimy mess".

During the weekend of June 13-14, 2015, a large swarm of mayflies caused several vehicular accidents on the Columbia–Wrightsville Bridge, carrying Pennsylvania Route 462 across the Susquehanna River between Columbia and Wrightsville, Pennsylvania. The bridge had to be closed twice during that period due to impaired visibility and obstructions posed by piles of the dead insects.

The American Sand-burrowing Mayfly (Dolania americana) has the shortest adult lifespan of any mayfly, and possibly any insect. The adult females of the species live for less than five minutes.

Adult males of some families have two large cylindrical "turban" eyes (also known as turbanate or turbinate eyes)that face upwards, in addition to their main eyes and ocelli. The turban eyes are capable of detecting ultraviolet light and are thought to be used during courtship to detect females flying above them.

Uniquely among insects, mayflies possess paired genitalia, with the male having two aedeagi (penis-like organs) and the female two gonopores (sexual openings). When your entire adult life revolves around making as many eggs as possible before dying, you have to be ready to do it from all sides. Follow bestanimal for more Penis Facts.

The Roman lawyer Cicero wrote philosophically of mayflies in his Tusculan Disputations: “Artistotle saith there is a kind of insect near the river Hypanis, which runs from a certain part of Europe into the Pontus, whose life consists but of one day; those that die at the eighth hour die in full age; those who die when the sun sets are very old, especially when the days are at the longest. Compare our longest life with eternity, and we shall be found almost as short-lived as those little animals.”

Mayflies are the primary source of models for artificial “flies”, hooks tied with coloured materials such as threads and feathers, intended to lure freshwater trout, used in “fly fishing.” In 1983, Patrick McCafferty recorded that artificial flies had been based on 36 genera of North American mayfly, from a total of 63 western species and 103 eastern/central species. A large number of these species have common names among fly fishermen, who need to develop a substantial knowledge of mayfly "habitat, distribution, seasonality, morphology, and behavior" in order to match precisely the look and movements of the insects that the local trout are expecting.

Mayflies are consumed in several cultures and are estimated to contain the most raw protein content of any edible insect by dry weight. In Malawi, kungu, a paste of mayflies (Caenis kungu) and mosquitoes is made into a cake for eating. Adult mayflies are collected and eaten in many parts of China and Japan. Near Lake Victoria, Povilla mayflies are collected, dried and preserved for use in food preparations.

The Holy Family with the Dragonfly (1495) is an engraving by German artist Albrecht Dürer (1471–1528) from approximately 1495. While the insect depicted in the engraving is commonly named as a dragonfly, or even argued to be a butterfly, it resembles a mayfly in wings and body. A similar engraving displayed in the National Gallery of Art in Washington, D.C. calls the piece The Holy Family with the Mayfly, explaining that the addition of a mayfly may signify the ephemeral nature of human life.

Mayfly nymphs process a great quantity of organic matter and transfer a lot of phosphates and nitrates to terrestrial environments when they emerge from the water, thus helping to remove pollutants from aqueous systems. The nymphs are eaten by a wide range of predators and form an important part of the aquatic food chain, while the adults also become food for thousands of terrestrial animals after they emerge.

The Large Blue Lake Mayfly (Tasmanophlebia lacuscoerulei), endemic to New South Wales in Australia, is listed as endangered, due to climate change. It is currently limited to a distribution of about 80 square kilometers in Kosciuszko National Park. Numbers of Blue-Winged Olive Mayfly (genus Baetis) have fallen dramatically, almost to none in some rivers. The Robust Burrowing Mayfly (Pentagenia robusta) and the Colorado Burrowing Mayfly (Ephemera compar), of the US, are believed to have gone extinct since the 1800s. It is hard to get reliable population data on mayflies, but many other species may be in significant decline, due to their nymphs being highly susceptible to aquatic pollutants including sewage, pesticides, and industrial waste. What is considered "modest levels" of pollution are sufficient to kill 80% of mayfly eggs. As important parts of the food chain, many other organisms can be drastically affected by a decline in mayfly populations, and without mayfly nymphs to graze on algae, algae can overwhelm areas where mayflies have disappeared.