The Art of Gliding on Water by Tiny Creatures

The Art of Gliding on Water by Tiny Creatures

Crossing a puddle might seem effortless to you, but for a tiny insect, it’s akin to scaling a slick and steep mountain. Two mathematicians have uncovered the precise mechanisms by which these minuscule creatures achieve this feat.

They exploit surface tension to their advantage, “gliding” across the water with almost no effort, according to John Bush from the Massachusetts Institute of Technology in Cambridge, Massachusetts, and his collaborator David Hu.

Water rises at the edges of puddles due to capillary action, causing the liquid near the boundary to curve upward. This phenomenon, known as the “meniscus,” is also commonly seen at the edges of a glass of water.

Larger insects, like water striders, are fast and big enough to sprint across the meniscus. Smaller creatures, however, lack the size and speed to do so. Instead, insects just a few millimeters in length deform the water’s surface with their legs, generating a force that “propels” them to the top of the meniscus.

Bush and Hu studied three species: Mesovelia and Microvelia (which walk on water as adults) and the larvae of the beetle Pyrrhalta. Using high-speed video, they recorded and analyzed the movements of these creatures.

All three groups of insects use their legs to pull the water’s surface upward in front and behind them while pressing their body’s middle section downward. The raised water under their legs becomes a region of particularly high surface tension. In other words, the meniscus at this point becomes very steep. Much like bubbles on the surface of champagne, the regions of high tension attract each other to minimize the overall surface tension. This attraction pulls the insect upward to the peak of the slope.

“They climb the meniscus and slide down under the force of gravity, then find a new position and repeat the process,” Bush explained.

According to Bush, the insect’s front legs play the primary role in this effect. The middle legs press downward to support their weight and prevent sinking, while the hind legs pull the insect upward, balancing the front legs to avoid slipping or tumbling backward.

This technique transforms them into agile acrobats. These insects can glide across the meniscus at speeds of up to 30 times their body length per second, far surpassing the human record of about five times body height.