Kobus Cilliers | On 29, Dec 2019

Darrell Mann

Stenocara gracilipes, also known as the fogstand beetle, is a species of beetle that is native to the Namib Desert of southern Africa. This is one of the most arid areas of the world, receiving only 14mm of rain per year. The beetle is able to survive by collecting water on its bumpy back surface from early morning fogs.

To drink water, the S. gracilipes stands on a small ridge of sand using its long, spindly legs. Facing into the breeze, with its body angled at 45°, the beetle catches fog droplets on its hardened wings. Its head faces upwind, and its stiff, bumpy outer wings are spread against the damp breeze. Minute water droplets (15-20 µm in diameter) from the fog gather on its wings; there the droplets stick to hydrophilic (water-loving) bumps, which are surrounded by waxy, hydrophobic troughs. Droplets flatten as they make contact with the hydrophilic surfaces, preventing them from being blown by wind and providing a surface for other droplets to attach. Accumulation continues until the combined droplet weight overcomes the water’s electrostatic attraction to the bumps as well as any opposing force of the wind; in a 30 km/h breeze, such a droplet would stick to the wing until it grows to roughly 5 mm in diameter; at that point it will roll down the beetle’s back to its mouthparts.

Nature is great at evolving high-functioning tribological surfaces, but the fogstand beetle may have evolved one of the most cunning. The contradiction to be solved in the Namib Desert revolves around the need to acquire water when the only available water is in the form of atmospheric fog. Here’s how we might map that problem onto the Contradiction Matrix:

The most cunning part of the fogstand beetle solution is all about Principle 3, Local Quality, where, specifically, the wing-cases feature a lattice of hydrophobic and hydrophilic regions:

There’s also a bit of Equipotentiality (Principle 12) in the way the surface tension forces at the hydrophilic regions cause the moisture to stick flat to the surface so it doesn’t get blown away, and in the Asymmetry (Principle 4) of standing at an angle so the agglomerated water droplets run towards the beetle’s mouth.

Expect to see a host of biomimetic versions of the same Principle 3 idea in the human engineered world in the not too distant future…