Desert-dwelling organisms often exhibit striking adaptations to their arid environs¿consider the superb water-storage capabilities enabled by the cactus's succulent stem. Now a new study has revealed an equally remarkable feature for water collection in beetles inhabiting southern Africa's Namib Desert. Scientists have long observed that certain beetles in this rainless region bow into the wind to collect drinking water from the early-morning fog on their backs, letting the mist form droplets that then roll down to their mouthparts. But exactly how the creature converts fog water into the relatively large droplets remained a mystery. Research published today in the journal Nature reveals that the beetle's bumpy outer covering does the trick. The finding could inspire designs for commercial water-collecting devices.
Andrew R. Parker and Chris R. Lawrence of the University of Oxford in England took a long, hard look at the surface of the fused overwings, or elytra, of a beetle belonging to the Stenocara genus. The elytra are covered with an array of bumps visible to the naked eye. But examined under a microscope, a more complex structure emerged. Whereas the peaks of the bumps appear smooth and naked, their sides and valleys are textured and coated in wax. This microstructure, the researchers report, creates a highly hydrophobic surface akin to that exhibited by lotus leaves, which are well known for their ability to repel raindrops. Video recordings showed that fog water settles on the water-loving, or hydrophilic, peaks and then forms fast-growing droplets that adhere to the elytra. Once the droplet's contact area covers the hydrophilic peak, "the ratio of its mass to its surface-contact area increases rapidly until the capillary force that attaches it to the surface is overcome," the authors write. "At this point, the droplet detaches and rolls down the tilted beetle's surface, guided by the slight purchase afforded by other peaks along its path.
"The design of this fog-collecting structure can be reproduced cheaply on a commercial scale and may find application in water-trapping tent and building coverings, for example, or in water condensers and engines," Parker and Lawrence note. Indeed, devices incorporating the beetle's elegant structure could help provide much-needed water for drinking and farming in regions deprived of rain.