Male Mayflies Skydive to Tell Females Apart in Dim Light
Get the Health newsletter
Daily health & science — research, biotech, public health, the studies worth knowing. Free.
- Samuel Fabian of the University of Oxford and colleagues at Imperial College London filmed mayfly swarms in 3D in Richmond, London, publishing in the Journal of Experimental Biology that the males' vertical flight pattern is a way to stay below females and avoid mistaking other males for mates.
- The common mayfly's vertical skydiving dance — a steep climb followed by a slow descent with wings and tail outstretched — has likely persisted for roughly 300 million years, making mayflies among the oldest winged insects on Earth and old enough to be referenced in the Epic of Gilgamesh.
- Males have almost no visual filter for mates, Fabian says, and will pursue objects as obviously wrong as a beach ball; the vertical flight path is essentially their only reliable way to sort sex in dim light when males and females look nearly identical.
- Adult mayflies live only a few hours to a few days, making rapid and accurate mate identification essential for passing on genes — a life-or-deadline pressure that likely drove the evolution of the swarms' sex-sorting flight geometry.
- A WildFish census of Britain's chalk streams from 2015 to 2021 found the country has lost an average of 41% of its mayfly species since 1998, with Janina Gray citing pollution, sediment runoff, reduced river flows, and rising water temperatures as the drivers.
- Other research cited in the piece suggests even modest pollution in many English rivers can kill up to 80% of mayfly eggs laid in riverbeds, raising the stakes for the 51 mayfly species known in Britain and roughly 3,000 species worldwide.
- A 2019 global review estimated 40% of the world's insects are in decline, and one study projects more than one in ten species could be lost by the end of the century, framing the Thames mayfly dance as a vanishing evolutionary relic.
Why it matters: Mayflies have performed this vertical mating dance for roughly 300 million years, but Britain's chalk streams have already lost 41% of their mayfly species since 1998. With modest pollution capable of killing 80% of eggs, the urban Thames spectacle Fabian urges Britons to enjoy is an evolutionary relic on a shrinking clock.
