A gecko running across water

A gecko uses a complex series of movements to splash across a laboratory tank. Credit: Pauline Jennings

Biophysics

Geckos slap their feet and swish their tails to race over water

Slender lizards can speed across a body of water faster than a young alligator can swim.

Geckos zoom over water using a unique combination of undulation, water-slapping and other motions.

Small, lightweight insects can glide atop water thanks to surface tension, a cohesive force between water molecules. Some larger creatures, such as the basilisk lizard (Basiliscus basiliscus), run across water by vigorously slapping the surface with their limbs.

Jasmine Nirody at the Rockefeller University in New York City, Robert Full at the University of California, Berkeley, and their colleagues found that geckos (Hemidactylus platyurus) rely on a complex mix of mechanisms. Geckos use basilisk-like slapping and stroking movements, creating underwater air pockets that propel them. Lifting their heads and chests out of the water reduces drag, and wriggling their bodies and submerged tails from side to side generates thrust. Surface tension also seems to give the animals a boost; when the researchers halved the surface tension of water using detergent, geckos slowed by 58% compared to controls.

The geckos could sprint across water at an average speed of around 62 centimetres per second. That’s faster than the swimming speed of young alligators.