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By Ivan Noble
BBC News Online science staff
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Scientists have
developed a robotic insect which walks on water.
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The insect's long hairy legs leave telltale
vortex trails in the water 
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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.
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Water striders are foraging insects which can
walk on water
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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, 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.
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