Friday, March 23, 2007

"Stenocara beetles, living in the harsh clime of the Namib desert in Namibia, use a unique adaptation on their exoskeletons to harvest water from occasional fog.

These beetles use rounded nodules, just 10 microns in size and arranged in a close-packed hexagonal pattern, embedded in a bumpy matrix. The nodules are coated in wax, while the larger surrounding bumps are wax-free. The wax-coated nodules exhibit strong water-repellent properties, like Teflon, while the relatively smooth, wax-free surfaces created by the larger surrounding bumps actually attract water. The combination of both surface types enables the beetle to drink in the Namib.

The Stenocara beetle, equipped with its hydrophilic-hydrophobic surface matrix, has evolved a droplet-growing system. As it tilts its body into the fog-laden wind, minute water droplets are repelled from the "mountain" sides and troughs (formed by the wax-coated nodules) towards the peaks, or wax-free bumps, where they soon become large drops. At around 5mm in diameter they roll down the beetle's back towards its mouth, guided by the slight purchase afforded by other "peaks" along its path. By this stage the drop is large enough to roll into a strong wind, and is not blown off the beetle. Five mm drops are formed on the beetle in a steady, self-replenishing stream (Parker, pers. com.).

What makes the Stenocara beetle's strategy so intriguing is that it takes advantage of the natural properties of water (to collect on surfaces, to "ball up" into coherent droplets, and to flow down-hill at the urging of gravity) to meet its hydration needs. The solution is simple, elegant, and largely a result of structure and posture with a bit of body-friendly chemistry thrown in. "

Cool, but who cares, you say? This has interesting applications for water gathering in arid regions for humans, using the same idea....

Oxford biologist Andrew Parker, with physicist Chris Lawrence, has duplicated and enlarged this design for tents and rooftops, increasing fog-harvesting efficiency. " Animals are master engineers, so we copy them," says Parker.

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