The thorny devil (Moloch horridus) is a small, spike-covered lizard found only in the arid and semi-arid regions of Australia. Despite its intimidating appearance and its genus name borrowed from a Canaanite deity, the thorny devil is a slow-moving, ant-eating specialist that rarely grows longer than about 20 centimeters. What makes it genuinely remarkable is a suite of survival adaptations suited to one of the driest environments on Earth, including a skin surface that can pull moisture from damp sand and channel it directly to the lizard’s mouth.
Where Thorny Devils Live
Thorny devils occupy the dry interior of Australia, ranging across the western half of the continent and into parts of central and southern Australia. Their preferred terrain is sandy desert, spinifex grassland, and scrubby mulga woodland. They avoid the tropical north and the wetter coastal strips, sticking to regions where rainfall is sparse and temperatures swing from scorching daytime highs above 40 °C to cool desert nights. The sandy soils matter because thorny devils dig shallow burrows to escape heat and cold, and the loose substrate is where they also bury their eggs.
Within these landscapes, thorny devils tend to favor open ground with scattered vegetation. They are ground-dwellers with no real climbing ability, and they rely on the open terrain to locate the ant trails that make up their diet. Their home ranges are relatively small, and individual lizards have been tracked moving only short distances over weeks, which makes sense for an animal whose food source is stationary ant nests rather than mobile prey.
A Diet Built Entirely Around Ants
Thorny devils are among the most specialized feeders in the reptile world. Their diet consists almost exclusively of ants, and they show a strong preference for small, slow-moving species. A single thorny devil can eat thousands of ants in a day, sitting beside a trail and lapping them up one by one with a short, sticky tongue. Feeding sessions can last for extended periods as the lizard methodically works its way through a column of ants traveling between nest and foraging site.
This extreme dietary specialization shapes much of the thorny devil’s anatomy and behavior. Its skull is compact and its jaws are relatively weak compared to lizards that eat beetles or other hard-bodied insects. The teeth are small and peg-like, designed for crushing tiny ant exoskeletons rather than biting through anything substantial. The slow, deliberate feeding style also means thorny devils spend a lot of time exposed and stationary, which puts pressure on their defensive adaptations to compensate.
Ant-eating specialization is not unique among lizards, but the thorny devil takes it to an extreme. Many other desert lizards include ants as part of a broader insect diet, while the thorny devil appears to have very little dietary flexibility. This narrow niche works well in the Australian interior, where ant populations are enormous and reliable, but it also means the lizard is tightly bound to habitats where those ant communities thrive.
How a Desert Lizard Drinks Through Its Skin
The thorny devil’s most celebrated adaptation is its ability to harvest water using its skin. In a landscape where standing water is vanishingly rare, this lizard has evolved a network of microscopic channels between its scales that can capture moisture and move it by capillary action all the way to the corners of its mouth. The system works without any muscular pumping. Water simply wicks along the channels the way ink climbs through blotting paper.
The skin’s surface is covered in overlapping scales, and between those scales sit narrow grooves that form an interconnected capillary network. When water contacts the skin, whether from dew, rain, or damp substrate, it is drawn into these channels almost immediately. Researchers have documented that a single water droplet placed on the skin is absorbed into the inter-scale channels within roughly one to two seconds, and the scale surfaces themselves stay dry while the water travels through the grooves beneath them.1PubMed Central. Adsorption and movement of water by skin of the Australian thorny devil (Agamidae: Moloch horridus) The micro-structured surface combined with the channel geometry is what drives this rapid capillary uptake.2PubMed. Cutaneous water collection by a moisture-harvesting lizard, the thorny devil (Moloch horridus)
Once in the channels, water spreads radially outward from the point of contact. Unlike some other moisture-harvesting lizards, the thorny devil’s capillary system does not show strong directionality. A droplet applied anywhere on the body spreads in all directions rather than being funneled preferentially toward the mouth.1PubMed Central. Adsorption and movement of water by skin of the Australian thorny devil (Agamidae: Moloch horridus) The water eventually reaches the jaw region, where the lizard uses rhythmic jaw movements to ingest it. Each jaw movement takes in only a tiny volume, about 0.7 microlitres, so drinking is a slow process that requires the capillary system to be well filled before the lizard can meaningfully hydrate.3Journal of Experimental Biology. Cutaneous water collection by a moisture-harvesting lizard, the thorny devil (Moloch horridus)
How Much Water the Skin Can Actually Collect
The capillary system sounds like a miracle solution for desert life, but the actual volumes involved reveal its limits. The total volume of water needed to completely fill the skin’s capillary network is about 3.2% of the lizard’s body mass. That is not trivial for a small animal, but filling the system depends heavily on the water source.
Laboratory experiments have shown that a thorny devil standing in shallow water can fill its capillary network completely and then drink from the captured water. But standing water is precisely what these lizards almost never encounter in the wild. When placed on nearly saturated moist sand, a more realistic desert scenario after rainfall, the lizards could only fill their channels to about 59% of capacity, and that was not enough to trigger drinking behavior. Condensation from warm humid air onto a cool lizard body was even less effective, filling the channels to roughly 0.2% of body weight, far too little for the lizard to drink from.3Journal of Experimental Biology. Cutaneous water collection by a moisture-harvesting lizard, the thorny devil (Moloch horridus)
These findings suggest that the capillary skin system is most useful during and immediately after rain events, when puddles or thoroughly wet sand provide enough moisture to charge the system fully. On dry days between rains, the system alone probably does not provide enough hydration. Thorny devils likely rely on the water content in their ant diet and on behavioral water-conservation strategies, like burrowing underground during the hottest hours, to bridge the gaps between rain events.
Armor, a False Head, and a Rocking Walk
The thorny devil’s namesake spines are its most visually striking feature, and they serve multiple defensive purposes. The spines are hard, sharp, and cover nearly every surface of the body, including the legs, tail, and the top of the head. For a small predator like a bird or a monitor lizard, swallowing a thorny devil would mean dealing with a mouthful of rigid points. The spines make the lizard a genuinely unpleasant meal.
Behind the head, on the back of the neck, sits a rounded, knob-like structure sometimes called a “false head.” When threatened, the thorny devil tucks its real head down between its front legs, presenting the false head to the predator. The false head is expendable compared to the real skull, and the posture protects the actual brain and sensory organs. Whether the false head truly deceives predators or simply makes the lizard harder to grip is debated, but the behavior is consistent and well documented across wild populations.
Color change adds another layer of defense. Thorny devils can shift between lighter and darker shades of brown, orange, and grey depending on temperature, time of day, and perceived threat. On cool mornings they tend to be darker, absorbing more heat. During midday or when startled, they often lighten. The color change is not as dramatic or rapid as a chameleon’s, but it does help the lizard blend into the sandy, reddish desert soils where it lives.
Then there is the walk. Thorny devils move with a distinctive slow, jerky, rocking motion, swaying forward and backward as they step. This gait is thought to mimic a leaf or piece of debris blowing in the wind, making the lizard less recognizable as a living animal to visually oriented predators. It is one of the more unusual locomotion strategies in the lizard world and gives the thorny devil a strangely mechanical quality when observed in the field.
Reproduction and Growth
Thorny devils mate in the Australian spring, roughly between August and December. Males seek out females and courtship involves head-bobbing displays and leg-waving, behaviors common across agamid lizards. After mating, the female digs a burrow in sandy soil and lays a clutch of three to ten eggs, which she then covers and abandons. Incubation takes several months, with hatchlings emerging during the warmer months.
Hatchlings are tiny, roughly 6 centimeters long, and already have functional spines. They are independent from birth and begin foraging for ants almost immediately. Growth is slow by lizard standards, and thorny devils may take several years to reach adult size. Their lifespan in the wild is estimated at around 15 to 20 years, which is long for a lizard of their size and reflects the low-energy lifestyle of an ant specialist in a stable desert environment.
Predation pressure is highest on juveniles, which are small enough to be taken by birds, snakes, and larger lizards. Adults are better protected by their size and spines, though large goannas and raptors can still take them. The slow reproductive rate, small clutch sizes, and long time to maturity mean that populations are sensitive to sustained predation pressure or habitat disruption, even if individual animals are tough survivors.
Conservation Status and Threats
The thorny devil is currently listed as least concern by the International Union for Conservation of Nature. Across much of its range in interior Australia, its habitat is relatively intact. The arid landscape that the species depends on has not been heavily converted for agriculture the way wetter coastal zones have, and the lizard’s specialized niche means it does not compete directly with most introduced species.
That said, a few threats do exist. Feral cats and foxes, both introduced to Australia by European settlers, prey on reptiles and have devastated populations of many small Australian animals. Road mortality is another concern in areas where highways cross thorny devil habitat, since the lizards are slow-moving and tend to bask on warm road surfaces. Habitat degradation from overgrazing by cattle and feral camels can reduce ant populations and alter the soil structure the lizards depend on for burrowing.
Climate change is a longer-term uncertainty. Desert-adapted animals are already living near the edge of thermal tolerance, and shifts in rainfall patterns could alter the availability of the rare rain events that thorny devils depend on for drinking. Whether thorny devil populations will be resilient to these changes or pushed into decline is not yet clear, and the species’ low profile means it receives less conservation attention than more charismatic Australian fauna like koalas or bilbies.
A Parallel Design on Another Continent
One of the more fascinating aspects of thorny devil biology is its resemblance to the Texas horned lizard (Phrynosoma cornutum) of North America. The two species are not closely related. Thorny devils are agamid lizards, while horned lizards are iguanians, and their lineages diverged deep in evolutionary history. Yet both have independently evolved remarkably similar body plans: flattened, round bodies covered in spines, ant-based diets, and skin capillary systems for harvesting water.
The water-harvesting systems are particularly interesting because the two species have arrived at similar channel-based solutions through different structural details. The thorny devil’s capillary network spreads water radially in all directions from the point of contact, while the Texas horned lizard’s system shows more directional transport, preferentially moving water toward the jaw.1PubMed Central. Adsorption and movement of water by skin of the Australian thorny devil (Agamidae: Moloch horridus) Both systems use capillary channels between overlapping scales, but the geometry and connectivity of those channels differ. This is a textbook case of convergent evolution, where unrelated organisms facing the same environmental challenges arrive at structurally similar but independently derived solutions.
The dietary convergence is equally striking. Both species sit beside ant trails and feed by lapping up individual ants, and both have evolved reduced jaw musculature and small, peg-like teeth suited to this feeding strategy. Even their defensive strategies overlap, with both relying on spines, cryptic coloration, and body flattening to avoid predators. The fact that two distantly related lizards on opposite sides of the planet have converged so closely on the same body plan speaks to how powerfully desert environments shape reptile evolution.
Engineering Inspired by Thorny Devil Skin
The thorny devil’s capillary water-harvesting system has drawn attention from materials scientists and engineers looking for ways to collect and move water without mechanical pumps. The basic principle, that a textured surface with correctly sized channels can move water passively through capillary forces, has potential applications in fog-harvesting materials, self-cooling surfaces, and microfluidic devices.
Researchers have studied the geometry of the inter-scale channels in detail, measuring capillary volumes and flow rates to understand what makes the system work at a physical level. The dorsal (back) skin holds about 5.76 microlitres of water per square centimetre, while the ventral (belly) skin holds about 4.45 microlitres per square centimetre. In practice, the channels fill to about half their capacity before water transport ceases, meaning the effective working volume is somewhat less than the theoretical maximum.1PubMed Central. Adsorption and movement of water by skin of the Australian thorny devil (Agamidae: Moloch horridus) These numbers give engineers concrete design targets for biomimetic surfaces.
Several research groups have created synthetic surfaces inspired by the thorny devil’s skin, using 3D printing and micro-fabrication techniques to replicate the overlapping-scale geometry. The goal is not to copy the lizard exactly but to extract the design principles that make passive water transport possible and adapt them for human-scale applications. One area of active interest is building materials that could harvest dew or fog in arid regions, providing small but meaningful water supplies to communities without access to conventional water infrastructure. The thorny devil evolved its solution over millions of years of natural selection; whether engineers can match its efficiency with manufactured materials remains an open and active question.