Some insects can be found in almost every habitat on our planet, no matter how extreme the conditions. The Namib Desert of Southern Africa is one of the driest spots on earth. Rain rarely falls. The primary source of moisture for animals and plants are fogs that bring moisture from the ocean.
The Stenocara Beetle, is a curious insect with an exoskeleton adapted for collecting water droplets from the fog. Early in the day, before the sun burns off the fog, the Stenocara beetles will climb to the top of a dune and assume a characteristic posture with their head down and their abdomen up in the air. The amazing structure of the cuticle encourages water droplets to condense on the cuticle, then roll down to the head where the beetle can ingest these precious water droplets. How does this unique surface work?
The cuticle of these beetles is mostly coated with waxes that form a superhydrophobic surface. The superhydrophobic coating prevents water from escaping from the inside of the insect through the cuticle. The same superhydrophobic surface will prevent water droplets from sticking to those parts of the cuticle. Once the droplets form on hydrophilic parts of the cuticle, they roll down the superhydrophobic channels toward the head and mouth.
The cuticle of the beetle is not uniform. On the superhydrophobic cuticle is an array of hydrophilic bumps, each about one tenth of a millimeter in diameter. The water droplets in the fog readily accumulate on the hydrophilic bumps. As the size of a droplet increases, the force of gravity eventually pulls it off the hydrophilic bump and onto the superhydrophobic channels on the cuticle. The large droplet will not stick to the superhydrophobic channels and roll down to the mouth.
Nanotechnology now makes it possible to create new types of coatings that can mimic the cuticle of the Stenocara beetle. These coatings have a variety of interesting properties including self cleaning surfaces. Water collects on the hydrophilic bumps as large droplets, that race down the superhydrophobic channels removing dust and microorganisms from the surface.
The process of water collection by the beetles is interesting to observe. Below is a link to a video on Youtube of the beetles collecting water.