Species: Thorny devil (Moloch horridus)
Habitat: Arid deserts and scrublands of Australia
What devilry is this? The thorny devil lizard uses its entire skin as a web of drinking straws to soak up water from soggy sand.
This allows it to drink with its feet and skin, which comes in handy in a desert – especially to a lizard with a mouth structure so specialised for eating ants that it cannot drink water directly.
“Thorny devils are one of the most fascinating species that collect and transport water with their skin,” says Philipp Comanns of RWTH Aachen University in Germany.
Comanns and his team examined six thorny devils (Moloch horridus) from Mount Gibson, Western Australia, in the lab to figure out where they get their water from.
When the researchers placed them in a water puddle, the lizards could drink through their feet: they started opening and closing their mouths within 10 seconds, as their skin channelled water from their feet into their mouths.
“But rain or water puddles rarely occur in their habitat,” says Comanns.
Dew does naturally form in deserts, though, as the temperature drops in the evening. Yet the team found that natural condensation or morning dew that formed on the lizards’ bodies could not provide enough water for them to drink. It did, however, make their skin “superhydrophilic” and ready to soak up water faster from moist sand.
His team found that only 59 per cent of the lizards’ drinking straws were saturated when the animals stood in the wettest sand. So drinking from soaked sand through the feet was not the whole story, either.
Finally, when the researchers placed moist sand on replicas of the skin, the straws fully filled with water.
In nature, these lizards often cover their backs with moist sand, which might allow them to absorb more water than by simply standing in the sand. “Damp sand from dew appears to be a major water source for thorny lizards,” Comanns says.
So how exactly does it drink?
Soaking it up
The thorny devil’s skin is covered in microscopic grooves between their overlapping scales, creating a network of drinking straws. These can take up water from any part of the body through capillary action, whereby water is drawn along a channel, even against the pull of gravity.
The water is then funnelled directly to the lizard’s mouth ready for drinking.
Only when their web of straws is completely filled with water – making up about 3 per cent of their body mass – do these spiky reptiles drink. When they do this, they stand stock-still while rhythmically opening and closing their mouths up to 2500 times an hour.
Other animals, such as Woodhouse’s toad, the file snake, and African and Asian elephants, can also hold water in their skins. However, they lack the ability to transport water towards their mouths. “These animals rather take up the water across their permeable skin,” says Comanns.
Understanding the water-collection mechanism in thorny devils could help conserve them, and might inspire technologies for gathering fresh water in deserts.
“Maybe there will be some sort of water-harvesting machines for deserts in the future,” he says.
Comanns has already used the way that the skin of Texas horned lizards funnel water towards their mouths in one direction as a model to create designs for useful products.
“We have been able to develop designs that could be applied in hygiene products or lubrication in car engines, based on how the skin of Texas horned lizards transports water,” he says. The design even won him and a team of collaborators an award last month.
Journal reference: Journal of Experimental Biology, DOI: 10.1242/jeb.148791