What the species is and where it came from
The thorny devil (Moloch horridus) is a solitary agamid lizard. It is the only species in its genus. It is endemic to Australia. John Edward Gray described it in 1841.
It grows up to 21 cm (8.3 in) in total length, tail included, and females are generally larger than males. It is also called the mountain devil, thorny lizard, thorny dragon and moloch; the two large horned scales on its head complete the look of a dragon or devil. Many taxonomists suspect another species in the genus may remain to be found in the wild, but for now it stands alone.
It is only distantly related to the morphologically similar North American horned lizards of the genus Phrynosoma, and the similarity is usually thought of as convergent evolution. The same hydrophilic moisture-harvesting physiology is characteristic of several of those horned lizards and of a number of other agamas, so the skin trick is not unique to it.
It usually lives in the arid scrubland and desert that covers most of central Australia, in sandplain and sandridge desert in the deep interior and in the mallee belt. In Western Australia its habitat coincides more with regions of sandy loam soils than with a particular climate.
How it works, in terms someone would actually use
It harvests water by touching damp sand or dew-covered surfaces. Ridged, hydrophilic scales draw moisture in. Capillary channels move it to the mouth.
The scales are ridged, so the lizard can collect water by touching it with any part of the body, usually the limbs. When trace amounts of water touch the skin, hexagonal microstructures on the scale surfaces fill with water and the surface becomes superhydrophilic. Moisture then spreads over a wider area and is taken up faster, through small channels between the scales.
The water travels passively through semi-tubular channels beneath the partially overlapping scales, in an asymmetric, interconnected system that extends over the whole body surface. The channels end at the mouth. When moisture is plentiful, as at a puddle, active drinking can be seen in the movement of the jaws.
The lizard rubs its body against moist ground and shovels damp sand onto its back. Absorption through sand is its main source of water. Dew that forms on its skin in the early morning is channelled to the mouth by gravity and capillary action, and in rain it can absorb water over its whole body.
What it gets right
It gets water collection right: no rain needed, no wells dug, no movement required beyond contact. It turns dry ground into a drink.
What it does not
It does not regulate body temperature with its spines. It does not eat anything but ants. It does not burrow or climb trees.
Ants are the staple. It mainly eats species such as Ochetellus flavipes and others from the genera Camponotus, Ectatomma, Iridomyrmex, Monomorium, Pheidole and Polyrhachis, and it often eats thousands in a day. It moves slowly in search of food, water and mates with an unusual gait of freezing and rocking.
Its defences are spines, which are hard and rather sharp and make it difficult to swallow, and a spiny false head of soft tissue on the back of the neck. Threatened, it lowers its real head between its front legs and presents the false one. Wild birds and goannas are among the predators that eat it.
What it changed
It redefined how we think about desert hydration in reptiles. It showed capillary transport can replace drinking behaviour entirely.
Who it is for, and who it is not
It is for field biologists, desert hikers, and evolutionary ecologists. It is not for gardeners, pet keepers, or coastal birdwatchers.
Is it worth your time
Yes—if you’re in arid central Australia and want to see a lizard that drinks through its skin.
