London, June 27 : US researchers say that they have figured out how some snails extraordinarily crawl upside down at the water's surface, which they cannot actually grip.
Eric Lauga of the University of California, San Diego says that water snails do so by creating little ripples in the surface, and transform them into a 'foothold'.
He and his colleagues studied the common freshwater snail Sorbeoconcha physidae, which crawl at a speed of 0.2 cm per second, and stay buoyant by trapping some air inside their shells.
The researchers observed that the snalils foot wrinkles into little rippling waves with a wavelength of about a millimetre, which produces corresponding waves in the mucus layer that it secretes between the foot and the air.
They say that surface tension constrains the deformation of the mucus, and causes parts of the mucus film to get squeezed, and parts to get stretched.
According to them, this creates a pressure difference that pushes the foot forwards.
The researchers believe that their findings may point to a new method of propulsion, reports Nature magazine.
Lauga's colleague Anette Hosoi, a researcher from the Massachusetts Institute of Technology in Cambridge, Massachusetts, has already copied the adhesive/lubricating propulsive method of land snails to drive a robotic device.
She says that it might be possible to build similar devices that walk on water, but this will require tricky mastery of buoyancy to keep them floating right at the water surface.
The study will be published in the journal Physics of Fluids.