Fog basking beetles and Namib dune bushman grass were collected in the Namib Desert (Beetles: 23°20′S, 14°47′E; Grass: 23°34′S, 15°03′E) and brought to Lund University in Sweden. All necessary permits were obtained for the described field studies. The collections of beetles and grass were done in collaboration with the National Museum of Namibia under permit issued to the museum by the Ministry of Environment and Tourism. In the laboratory the collected grass samples were kept fresh in a closed container at 5°C. The beetles were kept in sand-filled containers at 24°C, 12 h
12 h light
dark, and ca. 45% RH. All experiments were conducted within three weeks of collection. The fog collecting efficiency was tested by placing beetles killed by light freezing and 100 mm long sections of grass in a fog chamber. The fog chamber consisted of a 50 L refrigerator (Waves wc-16007) where temperature was kept between 10–15°C. This is comparable to the temperatures during a Namib Desert fog event 
. Fog travelling ca. 0.1 m/s was generated with a fog producing machine (325 ml per hour) (Super fog, Lucky Reptile). Beetles were positioned at the 23° angle previously established as the mean angle between horizontal and ventral body surface of O. unguicularis
in fog basking stance 
. The grass was positioned at the same angle. Eppendorf tubes were placed to catch water running off the experimental objects and fog water harvesting efficiency was measured as the amount of water collected in the tubes. To test for specialised surface properties of the grass, sections of metal wire (galvanized iron) with similar dimensions (length
100 mm and diameter
1.4 mm) were included in the experiments. Like the beetles and grass straws, the metal wires were also positioned at a 23° angle. In the first set of experiments, the three experimental objects (beetle, grass straw, and metal wire) were placed in a row in random order and exposed to fog for two hours. Twelve experiments were performed and each individual experimental object used only once.
The size of the surface area exposed to fog will affect the amount of water collected. To calculate water collection per mm2
we determined the upper surface area of the experimental objects. The upper surface area Au
of the grass straw and metal wire sections was calculated as: Au
π×Ø×L/2, where Ø and L is object diameter and length (L
100 mm). The diameter of the individual grass straw sections was measured with calipers. The upper surface area of the irregularly shaped beetles was determined by coating them with coloured latex and then photographing the latex casts pressed flat under a glass plate. A photo of a one cm2
coloured square was used as a reference and the number of coloured pixels converted into a measure of mm2
. The differences in the fog collecting efficiency between the three experimental object types were tested using ANOVA statistics and Tukey-Kramer Multiple Comparisons Post Hoc Test. The data were log transformed to pass Bartlett's test and Gaussian distribution was tested using the Kolmogorov–Smirnoff test. The results of the fog-water harvesting and the experimental object size calculations are all stated as mean values ± standard deviation.
In a second series of experiments, a set of twelve beetles were placed in the fog chamber and the amount of water collected after 0 to 120 minutes was measured in 20 minute increments. The six different experiment durations were presented in random order. The procedure was repeated with a set of twelve grass straws. The water run-off dynamics of the beetles and grass were compared using linear regression. An unpaired t-test with Welch correction was applied to test for difference in amount of fog water collected after two hours.