Desert beetle catches fog on its back

The nubbly back of a beetle in Africa’s Namib Desert has inspired a device for harvesting water from fog.

When a patch of dense fog rolls over the desert, the beetle, a species of the genus Stenocara, upends its body into a handstand. Fog droplets collect on its back and dribble into its mouth.

Now, Andrew R. Parker of the University of Oxford in England and Chris R. Lawrence of the technology company QinetiQ in Farnborough, England, have figured out how the fog catchers on the insects’ backs work. Manufacturers could readily mimic the texture in what could serve as fog-harvesting sheets, say the researchers in the Nov. 1 Nature.

The thumbnail-size beetle lives in a windy desert where rain is scarce but heavy fog is common. Bumps visible to the naked eye cover the insect’s back. Electron microscopy revealed a wax-coated carpet of tiny nodules covering the sides of the bumps and the valleys between them.

As fog wafts by, tiny water droplets gather on the top of a bump, merging into a drop big enough for the wind to nudge off the bump’s summit. The water slips down the waxy slope and rolls through water-repellant valleys until it reaches the beetle’s mouthparts.

The researchers mimicked the natural fog catcher by setting tiny glass beads into a wax surface. It collected more water than either plain glass or a flat wax coating. Parker says that technologies based on this concept might someday help reduce fog at airports and collect water for irrigation and drinking in those arid regions where fog is common.