The thorny devil, scientifically known as Moloch horridus, is classified within the kingdom Animalia, phylum Chordata, class Reptilia, order Squamata, suborder Iguania, family Agamidae, and subfamily Amphibolurinae. It is the sole species in the monotypic genus Moloch, established by John Edward Gray in 1841.
This lizard represents a case of convergent evolution with North American horned lizards of the genus Phrynosoma, sharing similar armored, ant-specialized adaptations despite distant relations. Unlike most Australian agamids, it lacks femoral pores and a supratemporal bone, features 21 presacral and 22 postsacral vertebrae, and has modified teeth for shearing ant exoskeletons, indicating a recent derivation from other arid-adapted agamids.
History
The thorny devil was first described in 1841 by British zoologist John Edward Gray, who named it after the ancient Canaanite deity Moloch, often depicted as a monstrous figure, combined with “horridus” meaning rough or bristly in Latin, to reflect its spiny appearance. Early observations noted its bizarre morphology, leading to common names like thorny dragon, mountain devil, thorny lizard, devil lizard, horned lizard, and thorny toad.
It remained relatively obscure until more ecological studies in the 20th century highlighted its unique adaptations, such as water-harvesting skin. Taxonomists have speculated about the potential existence of undiscovered related species in the wild, but none have been confirmed. During World War II, anecdotal reports mention scams where American servicemen in Australia were sold thorny weed fruits as “thorny devil eggs.”
Identifying Characteristics
The Thorny Devil is easily identified by its body. It has a body length up to 21 cm (including tail), with females typically larger (up to 110 mm snout-vent length and 88.7 g) than males (up to 96 mm and 49 g). Its most striking feature is the coverage of uncalcified conical spines and shields across the head, body, tail, and even ventral surfaces, providing camouflage in shades of brown, olive, tan, or yellow that shift with temperature—paler in warmth and darker in cold.
A prominent spiny “false head” on the neck, supported by soft tissue and bony bosses, serves as a decoy, while two large horned scales on the actual head enhance its devilish illusion. The lizard’s skin has ridged, hydrophilic scales with microstructures that facilitate capillary water collection from any body part to the mouth. It moves with a slow, rocking gait, often freezing to blend into surroundings, and exhibits sexual dimorphism in size but similar growth rates until the first year.
Habitat & Distribution
The thorny devil is endemic to Australia, primarily inhabiting the arid interior regions of Western Australia, South Australia, Northern Territory, and parts of Queensland, with a focus on sandy loam soils rather than specific climates. Its distribution spans sandplain and sandridge deserts, spinifex grasslands, mallee scrub, acacia woodlands, and shrublands, often in the Great Sandy Desert and mallee belt.
These lizards prefer habitats with Triodia grasses and acacia scrub, digging shallow burrows for shelter during extreme temperatures. They are semi-nomadic, with home ranges overlapping and limited daily movements (average 78 m), though they may travel farther during mating season.
Mating Habits
Mating habits occur mainly from August to December, during late winter to early summer, when males perform displays involving head-bobbing, leg-waving, and circling to attract females. Receptive females allow mounting, while unreceptive ones may roll or fall to dislodge males.
This species is oviparous and iteroparous, with females laying 3 to 10 eggs (median 8) in burrows up to 30 cm deep, often on south-facing sand ridges, after a gestation involving possible sperm storage. Eggs incubate for 90 to 132 days (mean 118), hatching in spring or summer.
Hatchlings are independent at birth, averaging 65 mm and 1.8 g, and receive no parental care beyond egg provisioning. Maturity is reached around age 3 to 5, with females experiencing significant weight loss (up to 42%) post-laying but recovering quickly.
Diet
The diet of the thorny devil is strictly myrmecophagous, consisting exclusively of ants, with preferences for genera like Iridomyrmex (especially I. rufoniger), Crematogaster, Camponotus, Pheidole, Monomorium, Polyrhachis, and Ectatomma. As sit-and-wait predators, they position near ant trails or shrubs, consuming 600 to 3,000 ants per meal at rates up to one per second, often in mornings or late afternoons above 24°C.
Their modified teeth shear through chitin, and large stomachs accommodate bulk intake, though they assimilate only about 59% of energy due to ants’ low nutritional value. Water is obtained via skin channels that direct dew, rain, or sand moisture to the mouth through capillary action, even against gravity.
Threats
Threats to the thorny devil include predation by birds like Australian bustards and black-breasted buzzards, reptiles such as goannas and snakes, and introduced mammals including dingoes, red foxes, and feral cats. Human activities pose indirect risks through habitat disturbance, vehicle strikes, and collection for the pet trade, though populations remain stable.
The lizard defends itself with spiny armor that deters swallowing, camouflage, freezing behavior, puffing up to appear larger, and presenting its false head while tucking the real one. It is also parasitized by nematodes and tapeworms, potentially transmitted via ants.
Conservation Measures
Conservation measures for the thorny devil are minimal due to its classification as Least Concern on the IUCN Red List, reflecting stable populations across a wide range and no major threats. It is not listed under CITES, but protections include habitat preservation in Australian reserves and regulations against illegal collection. Captive breeding in zoos aids research and education, promoting awareness of its adaptations. Monitoring continues to assess impacts from climate change, invasive species, and habitat fragmentation.
Other Facts
Other aspects of the thorny devil include its diurnal, solitary lifestyle with bimodal activity peaks in autumn and spring-summer, hibernating in burrows during extremes. It is heterothermic, regulating temperature through postural changes, and communicates via visual cues like head-bobbing.
Lifespan reaches 6 to 20 years in the wild, with body weight fluctuating up to 30%. Popular in zoos for its unique morphology, it has inspired studies on biomimicry for water collection and holds cultural significance in Australian folklore without negative human impacts.