American mathematicians made the robot after cracking the secret of how some insects glide across water. They wanted to prove that they had understood properly the physics behind the pond skater’s seemingly impossible movement. It had been thought that it simply made waves, but John Bush and colleagues at the Massachusetts Institute of Technology used high-speed video footage to show that pond skaters use their legs like rowing boat oars, creating swirling vortices below the surface that propel them forwards. They are kept afloat by their hairy legs and the viscosity of the water’s surface.

Michael Dickinson, a researcher, said: “It is the rearwards motions of these vortices that propel the animal forwards.”

The team produced mathematical formulae describing the motion, and used that knowledge to create the larger Robostrider. The report, published in the journal Nature, said: “Robostrider travels half a body length per stroke in a style less elegant than its natural counterpart.”