How basilisk lizards run on water

Settled in 1996 by James W. Glasheen and Thomas A. McMahon (Harvard University).

Central American folklore long celebrated the basilisk lizard's apparent ability to run on water, but the physical mechanism supporting an animal many times heavier than insects that use surface tension was unclear. Glasheen and McMahon combined force measurements from a physical model of the lizard's foot with high-speed video analysis of live basilisks, showing that for moderate-sized lizards most of the body weight is supported not by the initial slap but by the foot stroking downward while it creates and pushes off an air cavity beneath the water surface. Their 1996 Nature paper quantified how support mechanism shifts with lizard size, and subsequent studies (e.g., PNAS 2004) extended the three-dimensional force analysis. This established basilisk water-running as a well-understood case of dynamic (not static) surface support.

A lizard's party trick of sprinting across a pond turns out to be a carefully choreographed underwater push against a bubble of its own making, not a simple walk on surface tension.

Explanations that circulated

• The popular assumption that basilisks are supported purely by surface tension, like a water strider — surface tension is far too weak to support an animal this size; the Nature study showed support instead comes mainly from slapping and then stroking the foot down to create and push against an air cavity underwater

References

• A hydrodynamic model of locomotion in the Basilisk Lizard, James W. Glasheen, Thomas A. McMahon, Nature, 1996