The strange ability of a Namibian beetle to collect water droplets on its back from fast-drifting fog may have a serious commercial application.
Dr. Andrew Parker of Oxford University’s Department of Zoology and Dr. Chris Lawrence of QinetiQ (formerly DERA), Farnborough, are translating their observations of the Stenocara sp. beetle into a marketable system for ‘harvesting’ water for drinking or irrigation from the dense early morning fogs of certain deserts, where rainfall is virtually non-existent.
Water droplets in fog are so small and light that they blow almost horizontally in a breeze, but by tilting its body the Stenocara beetle can ‘grow’ larger droplets (of 5mm in diameter) on its back, which then roll to its mouth in a controlled way.
Dr. Parker and Dr. Lawrence noticed that the beetle’s mechanism for droplet formation involves a novel combination of surfaces on its back; a pattern of smooth, bare peaks are hydrophilic (water-attracting), while the troughs between are covered in flattened nodules with a further coating of wax, making these areas hydrophobic (water-repellent). Water molecules in the fog are attracted to the peaks, forming fast-growing droplets that ‘stick’ to the beetle’s back. When droplets reach a certain size, they become detached and roll down the tilted beetle, guided by the different textured surfaces. At this size they can even roll into a wind.
The researchers have found that this unique natural structure can be easily reproduced in sheet form via techniques such as injection moulding or printing, and have created a device that can collect vapours to provide water for drinking or farming.
Dr. Parker said: ‘Fog harvesting is a renewable technology that is already being used in 22 countries. One experimental system consists of netting vertically suspended in the path of a wind-blown fog, but the system mimicking Stenocara sp. is considerably more efficient. Also, it could be more resilient where applied to the roofs of buildings.’
The innovation provides a good example of biomimetics, where structures or behaviours in the natural world are reproduced for practical applications.
A patent for the system has already been applied for.