How the Namib desert beetle harvests fog

Partly settled. Some of it is understood, some is still argued about.

Desert naturalists had long noted that certain Namib Desert darkling beetles tilt their bodies into oncoming fog banks, apparently drinking condensed water, but the surface physics enabling this was undescribed until Parker and Lawrence's 2001 Nature paper proposed that alternating hydrophilic bumps and hydrophobic, wax-coated channels on the beetle's back both nucleate and then roll droplets toward its mouth. The paper became a landmark in biomimetic fog-harvesting materials research, but subsequent studies complicated the original picture: a 2014 study by Guadarrama-Cetina and colleagues found dew nucleates preferentially in the smoother valleys rather than on the bumps as originally proposed, and separate behavioral-ecology work has questioned how much wild beetles actually rely on this fog-basking posture in nature versus other water sources. The core surface-physics finding (patterned wettability aids condensation and collection) is well supported, but the original beetle-specific story has been partially revised and is not considered the final word.

A tiny beetle in one of Earth's driest deserts may have quietly evolved a patterned surface that modern engineers are still trying to fully reverse-engineer for fog-harvesting technology.

Explanations that circulated

• The beetle's whole back is uniformly water-attracting, and any bumpy dark surface in fog would work the same way — Parker & Lawrence's original model instead required alternating hydrophilic (wax-free) bumps and hydrophobic (waxy) channels; later work (Guadarrama-Cetina et al. 2014) showed dew actually nucleates preferentially in the smooth valleys due to microstructure differences, a more nuanced picture than the original 'bumps versus valleys' story, and other researchers (Hamilton and coauthors) have questioned whether wild beetles behaviorally perform the fog-basking posture described in the original account at all.

References

• Water capture by a desert beetle, A. R. Parker, C. R. Lawrence, Nature, 2001
• Dew condensation on desert beetle skin, A. Guadarrama-Cetina, A. Mongruel, W. Gonzalez-Vinas, D. Beysens, The European Physical Journal E, 2014