How to walk on water

Water is tricky, floppy stuff. As the National Geographic describes it, "Most animals that attempt to walk—or run—across water immediately sink toward their supporting limb because water, unlike solid ground, offers little support or resistance".

Most animals.

But some animals can move across water, along its surface. From skittering quickly across a lake to spinning around on a pond, being able to move along the water's surface gives some animals an advantage over their predators and prey. But how do they do it? Read on!

Surface tension enables animals to move along the surface of water. Image credit: José Manuel Suárez

Method 1: hang out in the surface tension.

Water molecules stick to each other more than they stick to molecules in air or on other surfaces, which creates an elastic effect at the water's surface called surface tension. If you are a small creature, such as an insect, spider or tiny lizard, you can increase the supportive properties of the water's surface using specially-adapted water repellent feet. Spiders in the genus Dolomedes (often called raft or fishing spiders) have a dense covering of hair all over their bodies, which traps air when it comes into contact with water. The larger Dolomedes spp. skate about on the water with all their legs, and their bodies, touching the surface. The smaller species can raise their legs to use as a sail. Pond skaters, mosquitoes, and even small geckos, can use a combination of hairs and waxes to form air cushions on their feet, which behave like little floaty slippers. However, if you are big, or have few feet, you won't be able to build up enough air beneath you to use this method.

Method 2: run really fast, slapping the water with your feet.

Are you a medium-sized animal with big feet? If so, this method of water-crossing may be for you! Basilisk lizards (genus Basiliscus) and some species of grebe (Aechmophorus spp.) are able to run across water by slapping it with their big feet, trapping air in pockets which keeps them near the surface. After its initial slap, the foot becomes submerged and performs a backwards stroke, propelling the animal upwards and forwards. For the lizards, dashing across the damp is a life-saving predator avoidance strategy. For the grebes, it's simply a sexy dance.

Method 3: Combine approaches for ultra-fast surface skittering.

If you are unsure what mode of water walking is for you, take some advice from an Asian house gecko (Hemidactylus platyurus). Research published this month shows that house geckos combine the above approaches, adding in semi-planing as a third trick. Integrating different methods of surface travel gives the geckos almost as much speed on water as they have on land. In addition to relying on surface tension and slapping the water with their weird little gecko feet, house geckos have flattened bodies and superhydrophobic (water-repellant) skin. All these adaptations work together to allow the lizard to semi-plane, and perhaps even hydroplane, with the front of its body lifted from the water and its tail providing propulsion from behind.

Weird little gecko feet. Image credit: Psumuseum.

Far from being restricted to messiahs and their disciples, walking on water is practised across the animal kingdom. Some animals make clever use of surface tension, others simply swim-walk rapidly along. New research reveals that house geckos combine these two approaches due to their intermediate size, adding semi-planing into the mix for extra speed. I hope this article has inspired you to strive to new levels of locomotion: all you need are a few adaptations and you, too, can skitter-surf in style.