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Last Updated: Wednesday, 6 August, 2003, 20:52 GMT 21:52 UK
Robot insect walks on water
By Ivan Noble
BBC News Online science staff

Scientists have developed a robotic insect which walks on water.

The insect's long hairy legs leave telltale vortex trails in the water

The team, based at the Massachusetts Institute of Technology (MIT) in the US, were testing out a theory about how one family of foraging insects performs the same trick.

Previous theories put forward to explain how water striders (Gerridae) manage to propel themselves across the surface of ponds and lakes had one major problem.

They predicted that young water striders should be too weak to move, while nature shows clearly that they are not.

Rowing and surface tension

Surface tension explains why water striders do not sink below the surface as they stand on water.

Water striders are foraging insects which can walk on water

But a careful experimental study was needed to explain how they propel themselves forward.

"What we did was to apply some conventional techniques of flow visualisation in fluid dynamics," MIT's John Bush told BBC News Online.

"You basically sprinkle dye or tiny particles into the water and record what happens with a high-speed camera."

Dr Bush and his collaborators, David Hu and Brian Chan, discovered that the secret to the water strider's locomotion is that it rows across the water without penetrating the surface.

Robostrider, MIT
Robostrider, the water strider's robotic counterpart
The rowing motion leaves a telltale vortex behind each foot, clearly visible on camera.

The robotic version of the water strider is bigger than its real-life counterpart and its motion less graceful, but it does seem to show that the MIT team has managed to capture the essence of a natural phenomenon.

Details of the research appear in the journal Nature.




WATCH AND LISTEN
Robostrider
See the robot in action



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