Beetle's Shell Offers Clues to Harvesting Water in the

Bijal P. Trivedi
for National Geographic Today
November 1, 2001

A beetle that lives in the Namib Desert, one of the hottest places on Earth, survives by using its bumpy shell to draw drinking water from periodic fog-laden winds. Scientists at the British Ministry of Defense are mimicking the shell's architecture to design more efficient water-harvesting techniques.

Zoologist Andrew Parker of the University of Oxford in the United Kingdom studied the Namibian desert beetle, Stenocara, and has figured out it captures water from the wind.

"To capture this water, you must be quite efficient," said Parker, who reported his findings in the November 1 issue of the journal Nature.

The surface of Stenocara's armor-like shell is covered with bumps. The peak of each bump is smooth, like glass, and attracts water. The slopes of each bump, and the troughs in between, are covered with wax, which repels water, like Teflon.

As morning fog sweeps across the desert floor, the water sticks to the peaks of Stenocara's bumps, eventually forming droplets. When the droplets become large and heavy enough, they roll down from the top of the peaks and are channeled to a spot on the beetle's back that leads straight to its mouth.

This water-collecting ability is critical to the beetle's survival because the Namib Desert is one of the most inhospitable places on Earth, with scorching sands that can reach 60 degrees Celsius (140 degrees Fahrenheit). Wind speeds approach gale force, and rainfall is rare. Short-lived early-morning fogs pass over the desert sands only about six times a month.

Parker thinks Stenocara's bumpy armor offers a good model for designing inexpensive tent coverings and roof tiles that could collect water for drinking and agriculture in arid regions.

Scientists at the UK's Ministry of Defense have already created prototypes of such surfaces. The results have shown that these surfaces are several times more effective than "net harvesting" methods used to collect water from fog in remote mountain towns of Peru and Chile.

Net harvesting is done by using fine polypropylene meshes stretched between two poles. Fog passes through the mesh, forming large drops of water which run down into a gutter leading to a reservoir.

"Net harvesting is a fairly crude and inefficient way of collecting water," said Parker. "There are more holes than net."

Parker became interested in Stenocara because of its high tolerance of heat. He originally searched for infrared reflectors on the beetle's shell that may help it survive in the Namib Desert by reflecting heat. Such reflectors, Parker thought, could possibly lead to the production of heat-resistant materials useful in fields such as rocket design.

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