The way Cheerios stick together has inspired a new kind of robot

The same phenomena that let beetles float across ponds and cause Cheerios to cluster together in your cereal bowl can be harnessed to make tiny floating robots. One of these, the Marangoni effect, arises when a fluid with a lower surface tension rapidly spreads out across the surface of a fluid with higher surface tension. This effect is exploited by Stenus beetles, which have evolved to zip across ponds by secreting a substance called stenusin, as well as soap-powered toy boats. To investigate how this could be used by engineers, Jackson Wilt at Harvard University and his colleagues 3D-printed round, plastic pucks around a centimetre in diameter. Inside each was an air chamber for buoyancy and a tiny fuel tank containing alcohol, which has a lower surface tension than water, in concentrations from 10 to 50 per cent.