Robotic water strider mimics nature with fan-like toes

August 25, 2025

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Though we have seen a quantity of completely different robotic water striders over time, scientists are nonetheless discovering intelligent new points of the bugs to copy. Lately, as an example, researchers created a strider-bot that zips throughout the water’s floor by way of followers on its toes.

Measuring solely 3 mm lengthy, water striders of the genus Rhagovelia actually are one thing particular.

On the ends of their two lengthy center legs – that are those they use for propulsion – there are feathery appendages which fan out upon hitting the water’s floor. Because the legs are then drawn again on the ahead stroke, these now-underwater followers cup the water just like the webs between a frog’s toes, quickly rowing the insect ahead.

Upon being drawn up out of the water on the finish of the stroke, the moist strands of the fan wick collectively into some extent – form of just like the bristles of a freshly dipped paintbrush. This makes the appendage extra streamlined because the leg swings again ahead, on its technique to execute one other stroke.

A fan-packin' Rhagovelia water strider – in this photo, the fan and claw are pointing downward and are reflected in the water's surface, which acts like a mirror — A fan-packin’ Rhagovelia water strider – on this photograph, the fan and claw are pointing downward and are mirrored within the water’s floor, which acts like a mirror

The followers permit the bugs to shoot throughout the floor at speeds of roughly 120 physique lengths per second. What’s extra, by deploying a single water-grabbing fan on only one facet, the striders can pull off 90-degree turns in about 50 milliseconds.

For sure, in case you had been designing aquatic robots, it will be nice if they had been so agile. With that thought in thoughts, scientists from the College of California-Berkeley, Korea’s Ajou College, and the Georgia Institute of Expertise determined to take a better take a look at Rhagovelia.

Using electron microscopy, Ajou’s Prof. Je-Sung Koh and postdoctoral researcher Dongjin Kim discovered that the person strands of every fan encompass a central flat, versatile, ribbon-like strip with smaller barbules branching off the perimeters of it – it truly is so much like a feather. This design permits the appendages to fan out underwater, to allow them to be used like an oar.

At left is a photo of the fan and claw at the end of Rhagovelia’s two oaring legs – at right, a colorized scanning electron microscope image of the fan shows the flat, ribbon-like microstructure of the barbs and the smaller barbules (green) that comprise the fan — At left is a photograph of the fan and claw on the finish of Rhagovelia’s two oaring legs – at proper, a colorized scanning electron microscope picture of the fan exhibits the flat, ribbon-like microstructure of the barbs and the smaller barbules (inexperienced) that comprise the fan

The scientists moreover found that the water’s floor rigidity supplies all of the elastic power that’s wanted to trigger the strands to fan out. It had beforehand been assumed that the fanning motion was muscle-powered. A small quantity of muscle energy is utilized to carry the followers tense in the course of the stroke, however none is used to deploy them.

Based mostly on these findings, the staff created a robotic model of the insect, named Rhagobot.

It is definitely greater than its namesake, coming in at 8 cm lengthy by 10 cm vast by 1.5 cm excessive (3.1 by 3.9 by 0.6 in). On the finish of every of its two center legs is a 1-milligram Rhagovelia-like fan – full with the flat-ribbon microarchitecture – measuring 10 by 5 mm.

The semi-aquatic robot Rhagobot (left) alongside a close-up of one its bio-inspired fans, which opens upon contact with water — The semi-aquatic robotic Rhagobot (left) alongside a close-up of 1 its bio-inspired followers, which opens upon contact with water

The entire bot, which is hardwired to an exterior energy supply, weighs simply one-fifth of a gram. It is presently able to scooting throughout the water’s floor at two physique lengths per second, and making 90-degree turns in lower than half a second. It’s hoped that descendants of Rhagobot will probably be even quicker and extra agile, making them helpful in purposes corresponding to search-and-rescue or environmental monitoring.

“Our robotic followers self-morph utilizing nothing however water floor forces and versatile geometry, similar to their organic counterparts,” says Prof. Koh, senior co-author of the research together with Georgia Tech’s Prof. Saad Bhamla. “It’s a type of mechanical embedded intelligence refined by nature by hundreds of thousands of years of evolution. In small-scale robotics, these sorts of environment friendly and distinctive mechanisms can be a key enabling expertise for overcoming limits in miniaturization of typical robots.”

A paper on the analysis, which was led by UC Berkeley’s Asst. Prof. Ortega-Jiménez, was just lately printed within the journal Science. You’ll be able to see Rhagobot in motion, within the video under.