Wildly Successful: The Thorny Devil

By Jim Knox

Never underestimate the power of a book to kindle interest in a young mind. On my seventh birthday, my mom and dad gave me a book on reptiles and amphibians of the world. I read it cover to cover…and on that front cover, was an illustration of a creature that fascinated me then, as it does to this day.

The Thorny Devil, Moloch horridus, looks more like a densely-thorned twig than an animal. With its scientific name inspired by John Milton’s poem, Paradise Lost, it is named after the horrible king, Moloch. Its Latin translation means rough, bristly, or dreadful. Also known as the Mountain Devil, Thorny Lizard, and Thorny Dragon, this small creature is a marvel of nature.

Native to vast arid sections of interior Australia, the devil’s habitat includes the shrublands and deserts of Western and Southern Australia. To cope with some of the planet’s harshest environmental conditions—that would prove fatal to other creatures—the Thorny Devil has evolved to possess a battery of behavioral and physical adaptations like no other.

Behaviorally, they are known as bimodal, switching from periods of high activity to complete inactivity. During the blazing Australian summer months of January and February, the devils retreat to the safety of underground burrows and lie dormant to avoid the lethal heat. Likewise, during the coldest months of June and July, the devils seek refuge in their burrows to conserve energy, reverting to near complete inactivity once again. For the remainder of the year, they emerge and respond to the relatively moderate environmental conditions.

So, how do these mysterious red and gold 8-inch-long reptiles survive in these inhospitable habitats? By mimicking the appearance of a benign thorny branch, and alternatively freezing and weaving, as if in response to wind, the devil attempts to fool potential predators and prey alike. Avoiding detection enables them to get down to the business of hunting. Not just any prey. These ambush hunters specialize. They are so special in fact, that they are classified as obligate myrmecophages, meaning they only eat ants. Exploiting the behavior of ants, which lay down chemical scent trails for members of the colony to follow, the devils detect an ant column and then ambush ant after ant with quick stabs of their sticky tongues. To overcome the challenge of snacking on hard-bodied chitinous prey, the devil possesses mandibular (upper) teeth which fit precisely within two maxillary (lower) teeth, creating a perfect ant-shearing device. Once their ant prey is detected, it is not unusual for a devil to consume several thousand tiny ants in a day!

Such adaptations certainly give the devil a survival advantage, but it is the devil’s namesake “Thorny” appearance that is a true evolutionary wonder. Possessing hundreds of modified thorny scales—some as large as rose thorns—the devil employs them in multiple ways. As a first line of defense, these hard, sharp projecting scales drop the devil way down on the menu for all but the most desperate of predators. If a predator does chomp down on a devil, beware. The devil can gulp air to expand its chest, transforming it into the terrestrial equivalent of a Porcupine Fish—making it one regretful mouthful! Yet these “thorns” are no mere haphazard defenses. They represent nothing less than an advanced hygroscopic (water-attracting) array. This network of tiny grooves between the thorny scales attracts and retains scarce desert moisture from the early morning dew that condenses on the devil’s body and funnels it by capillary action directly to its mouth! To further exploit its ability, the devil will brush up against plants, releasing even more dew to its grooves, for an additional drink.

Yet the devil’s adaptations don’t end there. With the ability to rapidly change color from dark olive-brown to bright brick-red and gold, the devil can further regulate its body temperature and metabolism in response to ambient temperatures. What’s more, these color changes enhance the lizard’s camouflage ability. If that wasn’t enough, the Mountain Devil possesses an additional adaptation which seems to prove the adage that “Two heads are better than one.”

When threatened, the devil drops its head down, and arches its neck up, revealing a knob-like mound of soft tissue which doubles as a false head—diverting predatory attention away from the devil’s head and directing it to its raised prominent spikes!

With such a host of adaptations, the Thorny Devil is equipped to engage a world of challenges head on. With a lifespan of 20 years or more, this little desert dweller proves that with the right attributes and a good plan, even the planet’s harshest of environments for the many, can be home sweet home for the few.

Jim Knox serves as the Curator of Education for Connecticut’s Beardsley Zoo and as a Science Adviser for The Bruce Museum. A Member of The Explorers Club, Jim shares his passion for wildlife conservation and education with audiences in Connecticut and beyond.

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