Move Over Dune Sandworms, These Desert Beetles Conjure Water from Thin Air

Beetles are fantastically adapted to surviving dry places. And one of the harshest for any beetle, or insect for that matter, has to be the Namib Desert. Stretching along the southwest African coast from Angola through Namibia and on to Cape Town, the Namib is but a hundred miles wide, where giant planes of gravel separate three seas of mobile sand blown in by the Atlantic Ocean. As deserts go, it is considered one of Earth’s oldest and gives rise to some of the planet’s tallest dunes – up to 820 ft. high, sculpted by harsh winds. Summer temperatures here reach 113°F and night-time temperatures can be as low as below freezing. And perhaps the most extreme aspect of all is that just ½ in. of rain falls there each year, sometimes none at all.

To a casual observer, the desert seems devoid of life. That’s because most of it lives 8 in. within the sand, sheltered from the surface heat and wind. In fact, fauna only come to the surface when they really have to. But what the apparently barren Namib lacks in rainfall it makes up for with a spectacular inland fog, which appears irregularly on the dunes, close to midnight. This extraordinary event arises from the north and west of Namibia, initially blowing in over the country as a high cirrus cloud drifting over the cold Benguela current of the Atlantic Ocean. The cloud becomes a moist fog in the high atmosphere, and upon intersecting land at a height of about 1,640 ft, it deposits fog droplets that can penetrate inland as far as 37 miles.

Although the Namib’s fogging event is highly variable and unpredictable, and only happens about once a month, the animals know to emerge just before or just as it arrives. It’s unclear as to how they accurately anticipate the fog, but Duncan Mitchell, an Emeritus Professor at the University of Witwatersrand in Johannesburg, South Africa, hypothesizes it may be down to them listening to the wind whilst they are protected down in the sand, since the wind changes direction just before the fog arises. But what can the fog do for them? In 1976, the answer was splashed across the covers of various scientific publications when Namib ecologist Dr. Mary K. Seely unravelled some of the intimate relationships between the fog and its fauna.

Born in America in 1939, Seely arrived in Namibia in 1967 as a post-doctoral student of Dr. Charles Koch, the then Director of the Desert Ecological Research Unit (which became known as Gobabeb). Just three years after Seely’s arrival she took over as Director – a major achievement at a time still plagued by horrific levels of sexism. The unit is now recognized globally as a center of excellence for its research and training. Six years after taking over as Director, Seely co-authored two papers with William Hamilton 3rd, one of which was published in Science magazine and one in Nature. It was these papers that first described a beetle’s extraordinary ability to harvest and collect water from fog. 

Seely and her team were the first to observe that some of the beetles were accessing fog water directly, by wallowing in it. She described how the beetles would emerge from the dune sand before the fog arrived – typically a few hours before midnight. They would then clamber clumsily (because of the cold) up the slip face to the crest of the dunes – that being the part of the dune where fog deposits best –and take up a head-stand posture with the elytra or wing case facing the wind bringing in the fog. And so they would wait, for three to four hours. It was the posture that helped them access the water, allowing fog droplets to deposit on their dorsal carapaces and then drip down towards the mouth, so long as the wind was not too strong and the fog was dense enough. It was an extraordinary discovery. Imagine watching the beautiful activity of these obsessive fog harvesters by torchlight. For 66 nights the researchers did just that.

The beetles appear to be all-consumed when a suitable fog blows in. Their sole aim is to harvest these droplets of water suspended in the air. Despite the abundance of plant detritus and other food above ground, they were never seen to feed during a fogging event, nor did they react to human observers nearby. Because they are cold and lethargic during their fog-basking, they would be vulnerable to nocturnal predators if such predators were prevalent. It is therefore likely that the evolution of their fog-basking behaviour, and indeed the behaviour of other active fog-harvesters, may depend on a low risk of predation, and especially of nocturnal predation.

It is Onymacris unguicularis (Haag, 1875), the head-stander beetle – looking more like a grasshopper than your average beetle with its very long back legs – that has adapted itself for true harvesting of atmospheric fog. Funny looking maybe, but it is perfectly suited for doing these handstands in the fog, and what’s more has specially adapted grooves in the exoskeleton that trap sufficient fog moisture for the water droplets to run down. These beetles are fast (the opposite of most tenebrionids), and personal experience of chasing after them but failing miserably is testament to this fact.

The fog-harvesting efficiency of the Onymacris Allard, 1885 beetle is down not only to the grooved nature of its exoskeleton, guiding the droplets of pure water to the insect’s mouth, but also the exoskeleton’s specific chemical make-up, according to Mitchell. Their back is hydrophobic, so it repels water, further encouraging it to run down the insect’s back. Although the beetles have never been observed drinking the water, it is known that water is getting into their mouths, as evidenced through the analysis of the chemical signature of the water and insect body fluids, as well as experiments using dead specimens in specially made fog chambers.

Seely and her collaborators scooped up these little marvels both pre and post fog in order to weigh them, thereby determining how much water they were taking in – the highest uptake they found generated a 30% change in body weight in one fog event. Thirty per cent! It’s an extraordinary amount of fluid, hugely efficient for an animal as small as a penny to sustain until whenever the next desert fogging event takes place. It is the equivalent of us drinking 20 liters of water (or just shy of 27 bottles of wine) in one go. This rapid acquisition potentially creates problems for storage and regulation of body fluids, but beetles have solved this in enterprising ways. Research shows that they keep this large amount of water separate from the rest of their body fluids. The fog water is incredibly pure, with virtually no electrolytes, so it has to be kept away from the rest of their circulatory system so as not to chronically dilute the animal. In the interval between fogs, as the insects become drier and drier, the water is then gradually introduced. Another solution is to isolate the fog water internally and then gradually to add osmolytes to it, only then allowing it to mix with other body fluids. This storage strategy has been reported for Onymacris unguicularis, which retains its harvested fog water in its gut. The effectiveness of this process is borne out in long-term studies of the population density of beetles in the Namib – fog-harvesting beetles maintain their numbers during dry periods, compared to others that lack this adaptation.

Other potential water-collecting surfaces, from other species, have also been investigated. One in particular, the bumpy back of a Stenocara Solier, 1835 beetle, piqued the interest of bioengineer Dr. Andrew Parker, and Chris Lawrence of Mechanical Services Sector, QinetiQ, a defence technology company, who published their findings in Nature, in 2001. Parker describes the back of a Stenocara as a mountain range with many peaks and valleys. The bumps or tops of the mountains are smooth with no waxy material on them, while the valleys and the sides of the mountains are lined with it. The smooth tops attract water and are super-hydrophilic (water loving) while the sides and bottoms are super-hydrophobic (water fearing). That bumpy surface, along with the wax, causes the accumulating water from the fog to ball up, that is, as the water hits the beetle’s back, it is propelled from those valleys to the peaks where a droplet forms, one that’s large enough and heavy enough to roll down to the beetle’s mouth. It is the combination of both a hydrophilic and hydrophobic surface that causes the drop to form.

A later publication identified their model species as Physasterna cribripes (Haag-Rutenberg, 1875), another tenebrionid, which looks very similar to Stenocara with its bumpy back, and as such their investigation into the impact of bumps is still pertinent. This paper by Thomas Norgaard and Marie Dacke, of the University of Lund, Sweden, published in 2010, looked at the water-collecting efficiency of the smooth-backed Onymacris unguicularis and another known fog-harvester Onymacris bicolor, along with the bumpy Stenocara gracilipes Solier, 1835 and Physasterna cribripes. Only the first two have been determined to harvest in nature but all offer the potential for bio-inspiration.

So what form could that bio-inspiration take then? Star Wars fans will remember Luke Skywalker’s moisture farm on the desert planet Tatooine – a series of huge white towers called moisture vaporators, which were used to capture moisture from the air. But could they work in real life, and help tackle growing global concerns of water scarcity? Armed with knowledge about the unique properties of the Stenocara beetle’s geometry, Parker began devising fog-capturing devices in sheet form, using 3D printing techniques. This technique prints layer upon layer to construct a three-dimensional object, hence the name. Parker has been looking at using hydrophobic inks on a hydrophilic surface to recreate the beetle’s strange but useful morphology. And you don’t have to limit this to the size of the beetle. They have hung up sheets in the Atacama Desert, the most arid of deserts but which can also be subject to fog, to harvest water from. The water drips down the sheet in to containers below. A single harvesting sheet averaging 50 sq m (538 sq ft) can, with optimal conditions, gather 1,000 l (220 gallons) of water in a single fogging session.

These are impressive figures, but the harvesting efficiency of these designs becomes compromised with an increase in sheet size, as the fog droplets have further to travel before reaching the collecting chamber, and so are more at risk of evaporation, particularly in warm windy conditions. Assistant Professor of Mechanical Engineering Dr. Kyoo-Chul Kenneth Park of Northwestern University, USA, has been looking at ways of overcoming fog-harvesting limitations at an industrial scale. He’s a self-professed Star Wars fan – on his desk sits a Lego model of one of Luke Skywalker’s moisture vaporators – inspiration perhaps to push this futuristic technology still further! Park has been adopting a multi-bioinspired approach to the problem, drawing on clever strategies employed by particular flora and fauna in both desert and rainforest environments. He’s developed fog-harvesting designs that use a surface structure with slippery asymmetric bumps. These not only incorporate the Namib Desert beetle’s efficient formation of droplets, they also borrow structures seen on the asymmetric spines of cactus plants, and the unique slipperiness of the rimmed surface of a pitcher plant. When combined, these features make for a fast continuous, directional transport of water in a minimal amount of time, thereby reducing water loss through evaporation. This strategy could, Park hopes, enable a wide range of water-harvesting applications on a larger scale.

Park also wants to apply his work to a new frontier – smog harvesting. With 4.2 million people dying each year from outdoor air pollution, according to the World Health Organization, extracting smog from the air in major cities could help tackle growing health and environmental challenges. Smog is a combination of fog and smoke, and capturing it is currently a far more difficult process than extracting water from fog, because water in the air clogs up the smog-filtering devices. But Park argues that instead of condensing fog, it is feasible to capture smog in the same way. Not just that, he is also exploring how to use smog-harvesting technology to tackle another one of the great challenges that has eluded many technological efforts – reducing the discharge of brine into the ocean by desalination plants. He’s hoping the technology will soon prove to be more than mere science fiction.

But back in the present, fog-capturing devices inspired by a beetle’s back are becoming a major industrial enterprise for sourcing freshwater in drought-stricken areas of our planet, where the right mix of geography and climate can be found. But with global warming, the fogs are disappearing. And with that, much of the Namib fauna is threatened with extinction. Despite this climate uncertainty, beetles have another trick up their sleeve that could point to their desert survival in the longer term, were the chances to harvest fog to become even less frequent. It lies in the design of the beetle’s bottom. The beetle's rectum does the same job as the rectum of most mammals or insects – absorbing nutrients and water from bodily waste before it is expelled. But beetles do it better than other species, and as a result, beetle feces are practically bone-dry. A big part of how they do this is down to the design of the beetle’s organs. Unlike in mammals, the beetle has kidneylike organs called malpighian tubules (named after Malpighi who first drew them) closely applied to its rectum, and the entire structure is encased in a chamber by a membrane. This allows the animal to generate high salt concentrations in the tubules, enabling the beetle to extract all the water from its feces by osmosis and recycle the moisture back into its body. It is also able to open its rectum in high humidity, allowing it to take water in and, again, almost fully absorb it into itself.

While scientists have been aware of this unique approach to water consumption for more than a century, only recently has Dr. Muhammad Naseem and a group of collaborators from the University of Copenhagen, Denmark, as well as the University of Edinburgh, UK, and the University of Glasgow, UK, been able to shed light on the underlying mechanisms involved. They studied red flour beetles Tribolium castaneum (Herbst, 1797), considered model organisms because they are easy to work with and share biological similarities with other beetle species. The researchers discovered a gene expressed at 60 times higher levels in the beetle’s rectum than in other parts of its body. This gene led them to discover a distinct group of cells positioned like windows between a beetle’s malpighian tubules and its circulatory system or blood, which have been found to play a crucial role in the beetle’s water absorption process through its rear end. As the beetle’s tubules surround its hindgut, these cells pump salts into the kidneys, allowing them to take in water from moist air through the rectum and into the beetle’s body.

With climate change, it is conceivable that opportunities to tap into the ethereal power of fog may slip beyond our reach. But the legacy of both the beetle bump geometry, and the grooved back of the headstander Onymacris beetle, will live on. Labs have been developing a host of applications that mix water-attracting and water-repelling surfaces, such as windows and mirrors that don’t fog up, or self-filling water bottles. An intriguingly simple model for a self-filling water bottle, created by South Korean industrial and graphic designer Kitae Pak, consists of a stainless-steel dome that adopts the simple groove principle of the Onymacris body. The Dew Bank Bottle is meant to be placed outside in the evening. In the morning, when the surrounding air begins to warm, water droplets condense to the steel surface of the bottle, which has become cold overnight. The dewdrops collected are then channeled down grooves in the surface design, to an enclosed circular holding-chamber. The designer expects that this device would gather enough moisture for a full glass of water per use.

Parker highlights how the beetle bumps can help recapture valuable water from air-conditioning units. In Japan for example, large air conditioning systems within city buildings consist of a central tower, resembling and acting like an exhaust that sends water vapor out into the atmosphere. This causes the urban air to rise in temperature by up to two degrees, which is both harmful and wasteful. If, as he suggests, we instead coat the towers with the ‘beetle bumps’ we could recapture the water, but also prevent the heat entering the environment that would significantly help reduce the temperature of the urban environment. Let’s drink to that!

Metamorphosis: How Insects Are Changing Our World by Erica McAlister with Adrian Washbourne is available from Smithsonian Books. Visit Smithsonian Books’ website to learn more about its publications and a full list of titles. 

Excerpt condensed for print from Metamorphosis © The Trustees of the Natural History Museum, London, 2024