How Do Thorny Devils Drink? Water Wicked Through the Skin

How the thorny devil’s skin moves water

The thorny devil lives in some of the driest parts of Australia, where open water is rare and may last only hours after a storm. Its answer is a built-in plumbing system on the outside of its body.

The scales overlap slightly, and beneath their edges run narrow, half-open channels. These channels connect with one another across the entire body, from the feet and legs, over the flanks and back, and onto the head, where they end at the corners of the mouth. When any part of the lizard touches water, the channels draw it in.

The force at work is capillary action, the same effect that pulls water up a thin glass tube or into a paper towel. Water molecules cling to the channel walls and to each other, so water creeps along narrow spaces even uphill, against gravity. That is why a thorny devil standing with only its feet in a puddle can still move water up its legs and along its body.

A skin built to love water

The surfaces of the scales are covered in a fine honeycomb pattern of microscopic ridges. Studies of thorny devil skin found that this texture makes the surface superhydrophilic, meaning that water spreads out into a thin film instead of beading up. Once the skin is slightly wet, more water spreads rapidly across it and flows into the channels.

The channels themselves have a layered design. Using micro-CT scans and electron microscopes, a 2017 study by Philipp Comanns and colleagues showed that each large channel between the scales is divided by small projections into finer sub-channels. The large channel takes up water quickly, while the smaller ones extend the distance water can travel by roughly 39%, which may reduce how much water the lizard needs before it can drink.

In the thorny devil, water spreads out in all directions from where it lands. This differs from the Texas horned lizard of North America, whose skin channels are shaped to send water toward the head.

When does the thorny devil actually drink?

Water reaching the mouth is not enough on its own. The thorny devil has to fill its channels first, and a 2016 study found that the complete network holds water equal to about 3.2% of the lizard’s body mass. Once the system is full, extra water reaches the mouth and the lizard begins to drink, swallowing small amounts with repeated jaw movements, roughly 0.7 microliters per gulp in the laboratory.

The same study tested the possible water sources one by one:

The researchers concluded that rain and moist sand are probably the thorny devil’s regular water sources. In the wild, thorny devils have been seen flicking damp sand onto their backs with their legs and rubbing their bodies against wet ground, behavior that fits these results.

What about dew?

Many books and websites say that thorny devils drink the morning dew that forms on their spines. Dew may help a little, and older field observations describe lizards gaining water from dew and rain. But the 2016 experiments showed that condensation on the skin alone fills only a small part of the channel system, well short of what is needed to start drinking.

That does not mean dew is useless. A thin film of water on the skin may help the channels fill faster when the lizard later touches damp sand or rain. The thorny devil probably combines several sources, taking whatever water its desert habitat offers. Like many desert reptiles, it probably also gets some moisture from its food, which in its case means ants, eaten by the hundreds, as explained in What do thorny devils eat?.

How scientists discovered the trick

The thorny devil’s unusual drinking was first studied in the laboratory by P. J. Bentley and W. F. Blumer, who reported in the journal Nature in 1962 that the lizard takes up water through capillary action in its skin. Later researchers revisited the mechanism. From 2011 onward, Philipp Comanns and colleagues in Germany, later joined by Australian zoologist Philip Withers, used high-speed video, skin replicas and imaging to measure exactly how the system works.

Their findings also showed that live animals were needed for accurate results: preserved museum specimens did not give the same measurements as living lizards.

Other lizards that drink with their skin

Thorny devils are not alone. The same kind of moisture-harvesting skin has evolved separately in several desert lizards on different continents, including the Texas horned lizard, the desert horned lizard and the roundtail horned lizard of North America, and toad-headed agamas of Arabia and Central Asia. These lizards are not closely related, so the shared trait is an example of convergent evolution: similar problems leading to similar solutions.

Engineers have taken note too. The thorny devil’s water-wicking skin has inspired designs for surfaces that move liquid without pumps, including an experimental swallowable medical capsule developed at MIT and described in 2023. Desert survival is a major theme among desert animals, but few solve it as elegantly as this small, spiky lizard.