O n a spring evening along the banks of the River Thames, thousands of mayflies can be seen engaging in what may be one of the world’s oldest dances. In the fading light, the males make a steep vertical climb, flip over and float back to Earth – wings and tail outstretched in a skydiving posture so as to drop slowly through the sky. Mayflies are among the world’s oldest winged insects, emerging roughly 300m years ago – long before dinosaurs walked the Earth. Even the Mesopotamian poem the Epic of Gilgamesh, one of the oldest pieces of literature, makes reference to the short-lived mayfly. Over the epochs, the insect’s basic design has changed very little compared with the fossils of their ancestors. “They have retained these odd characteristics and we can probably assume that they’ve been doing this [dance] for hundreds of millions of years, and yet we don’t really know why,” says Samuel Fabian, a research fellow at the University of Oxford who studies the aerial behaviours of insects.…