Darkling beetles (family Tenebrionidae) of the Namib Desert, located on the southwest coast of Africa, live in one of the driest habitats in the world. But some species of Darkling beetle can get the water they need from dew and ocean fog, using their very own body surfaces. Several researchers are studying the beetles, as well as synthetic surfaces inspired by the beetle’s body, to uncover the roles that structure, chemistry, and behavior play in capturing water from the air. Micro-sized grooves or bumps on the beetle’s hardened forewings can help condense and direct water toward the beetle’s awaiting mouth, while a combination of hydrophilic (water attracting) and hydrophobic (water repelling) areas on these structures may increase fog- and dew-harvesting efficiency. For certain species of Darkling beetle, the act of facing into the foggy wind and sticking its rear end up in the air (known as fog-basking behavior) is thought to be just as important as body surface structure for successfully harvesting water from the air.
Water balance and osmoregulation in Physadesmia globosa, a diurnal tenebrionid beetle from the Namib desertJournal of Insect PhysiologyOctober 24, 2003
“The Namib Desert has a remarkably high variety of Darkling beetles (Tenebrionidae) and a handful of them actively exploit fog for water intake [5,6]. Some of these construct sand trenches or ridges to catch the fog, while Onymacris unguicularis and O. bicolor instead utilise their own body surface as a fog water collector [7-9]. By adopting a head standing posture facing into the wind, the fog water collects on their elytra and runs down to their mouth, to be imbibed by the beetles. This unique behaviour is termed fog-basking . The advantage of fog collection for water intake in the extremely arid desert is obvious, and becomes critical when rainfall is absent over prolonged periods of time. Long term studies on the population density of Darkling beetles in the Namib Desert clearly shows that the fog collecting beetles are still present in great numbers during periods of low rain fall, whereas the large majority of Darkling beetles that lack this adaptation disappear or decline to less than 1% of their mean abundance .” (Norgaard and Dacke 2010:1-2)
Fog-basking behaviour and water collection efficiency in Namib Desert Darkling beetlesFront ZoolJuly 20, 2010
Fog collection by Namib Desert beetles
Irregular fog as a water source for desert dune beetlesOecologiaOctober 29, 2004
“…we investigated…the wetting and structural properties, of the surface of the elytra of a preserved specimen of Physasterna cribripes (Tenebrionidæ) beetle, where the macro-structure appears as a series of “bumps”, with “valleys” between them. Dew formation experiments were carried out in a condensation chamber. The surface properties (infra-red emissivity, wetting properties) were dominated by the wax at the elytra surface and, to a lower extent, its micro-structure… Dew formation occurred on the insect’s elytra, which can be explained by these surface properties. From the surface coverage of the condensed drops it was found that dew forms primarily in the valleys between the bumps. The difference in droplet nucleation rate between bumps and valleys can be attributed to the hexagonal microstructure on the surface of the valleys, whereas the surface of the bumps is smooth. The drops can slide when they reach a critical size, and be collected at the insect’s mouth.” (Guadarrama et al. 2014)