Lizards that live in deserts do not roam to find water. Even if they stay still, water in the soil under their feet travels to their mouths. A Korean research team revealed how lizards swallow the water gathered around their mouths. The findings are expected to solve a long-standing biological puzzle and be used in a device that obtains clean drinking water from contaminated soil.
Seoul National University College of Engineering said on the 6th that "a research team led by Professor Kim Ho-young of the Department of Mechanical Engineering and Professor Kim Sung-jae of the Department of Electrical and Computer Engineering has, for the first time in the world, identified the physical principle by which the desert horned lizard drinks water and, by mimicking it, developed a moisture collection system that can collect clean drinking water from contaminated soil." The results were published on the 22nd in PNAS.
◇Microscopic channels between scales draw in water
When it rains or the soil is wet, the desert horned lizard draws moisture up to the tip of its head through microscopic channels on the skin surface. It is the same capillary phenomenon that carries water absorbed by plant roots to the leaves. The microscopic channels, 100 μm (micrometer, one-millionth of a meter) wide, lie beneath the overlapping structure between scales. But how the lizard swallows the water thus gathered around the mouth had remained a mystery for decades.
The researchers filmed with a high-speed camera how the lizard swallows the water gathered around its mouth. The lizard slowly opened its jaws so the water would not remain on the jaw surface but collect at the corners of the mouth. "An analysis based on fluid dynamics showed that the slower the mouth opens, the less moisture is lost around the jaw," the team said. It is the same principle as when two wet plastic sheets are pulled apart slowly, the water gathers well to one side, but if pulled apart quickly, the water remains thinly smeared here and there.
The motion of slowly opening and then quickly closing the jaws acts as a biological pump that efficiently swallows water drawn from wet soil. As the skin around the corners of the mouth folds inward, it squeezes the collected water into the mouth.
The team developed a device that mimics the lizard's moisture-harvesting motion. A sponge riddled with microscopic pores absorbs moisture from the soil, and a motor asymmetrically opens and closes an artificial jaw like a lizard to collect the water. The researchers said the moisture collection method that mimics the lizard's jaw joint was more energy-efficient than the conventional approach of simply compressing a sponge to wring out water.
◇Combined with a purification unit, applicable to contaminated soil
The researchers coated the inside of the sponge with an ion exchange material, achieving simultaneous moisture collection and purification of more than 95% of harmful heavy metals. This means that even contaminated ground can yield clean drinking water if it is wet.
Professor Kim Ho-young said, "We have fluid-dynamically identified the wondrous survival strategy of desert lizards that had long been shrouded in mystery and developed machinery and equipment that uses it," adding, "It will be an important source for next-generation technology to secure water resources that can ensure safe drinking water with low energy consumption even in extremely arid environments or severely contaminated soil."
Scientists have long looked to desert-dwelling animals for ways to obtain water. A representative example is the beetle that lives in the Namib Desert of southern Africa. Although it is a desert, winds sometimes blow in from the sea laden with water vapor, bringing heavy fog. On foggy mornings, the beetle stands on its head. Droplets then form on the bumps on its back and roll into its mouth.
Researchers at MIT created a film that makes water from fog by mimicking the back structure of the desert beetle. They made a film of polymer material with microscopic bumps like the beetle's back. Using the same method, they also developed a coating that prevents bacteria from adhering. When the water droplets formed on the bumps roll off, dirt and bacteria are swept away with them.
Unlike the beetle, which gathers water vapor to make liquid water, the desert horned lizard draws rainwater or moisture from wet soil through microscopic skin channels, so the principle is different. If devices are developed to collect water by the beetle method when there is fog and by the lizard method when it rains, water collection efficiency in deserts can be maximized.
Professor Kim Sung-jae, a corresponding co-author, said, "Just as one travels short distances by taxi and long distances by airplane, drinking water can be purified in various ways depending on the amount," adding, "This technology can be applied to compact purification devices that secure a minimum supply of drinking water in resource-scarce environments."
The first author of the paper is researcher Kim Sung-ju, a doctoral candidate in the Department of Mechanical Engineering at Seoul National University. Professor Jung So-hyun of the Department of Robotics and Mechatronics Engineering at Daegu Gyeongbuk Institute of Science and Technology (DGIST) and Professor Kim Won-jung of the Department of Mechanical Engineering at Yonsei University were also listed as corresponding co-authors.
References
PNAS (2026), DOI: https://doi.org/10.1073/pnas.2609344123