Lizards that live in the desert do not roam to find water. Even if they stay still, water from the soil under their feet reaches their mouths. A domestic research team revealed how lizards swallow the water they collect at the corners of their mouths. The findings are expected to both solve a biological puzzle and be used as a device to obtain clean drinking water from contaminated soil.
The College of Engineering at Seoul National University said on the 6th that a team led by Mechanical Engineering Professor Kim Ho-young and Electrical and Computer Engineering Professor Kim Seong-jae was the first in the world to identify the physical principle behind how the desert horned lizard drinks water and, by mimicking it, developed a moisture collection system that can gather clean drinking water from contaminated soil. The results were published on the 22nd of last month in the Proceedings of the National Academy of Sciences (PNAS).
◇Tiny 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 microchannels on its skin surface. It is a capillary phenomenon like water absorbed by plant roots reaching the leaves. The microchannels, 100 μm (micrometers, one-millionth of a meter) wide, lie beneath overlapping structures between the scales. But how the lizard swallows the water collected at the corners of its mouth had remained a mystery for decades.
The researchers used a high-speed camera to film the lizard swallowing water collected at the corners of its mouth. The lizard slowly opened its jaws so the water would not remain on the jaw surface but gather at the mouth corners. The team said, "An analysis based on fluid dynamics showed that the slower the mouth opens, the less moisture is lost around the jaw." It is the same principle as when two sheets of plastic with water between them are pulled apart slowly, the water gathers well to one side, but if pulled apart quickly, the water is left as thin films here and there.
The motion of opening the jaw slowly and then closing it quickly acts as a bio-pump that lets the lizard efficiently swallow water drawn up from wet soil. As the skin around the mouth corners folds inward, it squeezes the water gathered there into the mouth.
The team developed a device that mimics the lizard's moisture-harvesting motion. A sponge riddled with microholes absorbs moisture from the soil, and a motor asymmetrically opens and closes an artificial jaw like a lizard's 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 purification, applicable even to polluted soil
The researchers coated the inside of the sponge with an ion exchange material to collect moisture and at the same time remove more than 95% of harmful heavy metals. It means that even on contaminated ground, if it is wet, clean drinking water can be obtained.
Professor Kim Ho-young said, "We have used fluid dynamics to clarify the long-veiled, astonishing survival strategy of desert lizards and developed machinery and equipment based on it," adding, "It will be an important source for next-generation water resources technologies that can secure safe drinking water with low energy use even in extremely arid environments or severely contaminated soils."
Scientists have long sought ways to obtain water from animals living in deserts. A prime example is a 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. Then droplets form on the bumps on its back and roll down into its mouth.
Researchers at the Massachusetts Institute of Technology (MIT) created a film that makes water from fog by mimicking the back structure of desert-dwelling beetles. They made a polymer film with fine protrusions like those on the beetle's back. Using the same approach, they also developed a coating that prevents bacteria from sticking. When droplets that form on the protrusions roll off, grime and bacteria are swept away with them.
Unlike the beetle, the desert horned lizard does not collect vapor to make water; it draws rainwater or moisture from wet soil through microchannels in its skin, a different principle. If a device is developed to collect water by the beetle method when there is fog and to follow the lizard when it rains, the efficiency of obtaining water in deserts can be maximized.
Co-corresponding author Professor Kim Seong-jae said, "Just as people take a taxi for short distances and a plane for long distances, drinking water can be purified in different ways depending on the amount," adding, "This technology can be applied to compact purification devices that secure a minimum amount of drinking water in resource-limited environments."
The first author of the paper is Lee Sung-joo, a doctoral researcher in the Department of Mechanical Engineering at Seoul National University. Professor Jeong So-hyeon of the Department of Robotics and Mechatronics Engineering at Daegu Gyeongbuk Institute of Science and Technology (DGIST) and Professor Kim Won-jeong of the Department of Mechanical Engineering at Yonsei University were also listed as co-corresponding authors.
References
PNAS (2026), DOI: https://doi.org/10.1073/pnas.2609344123