Molecular research suggests that, despite their extreme morphological changes from the primitive agamid morphology, thorny devils are relatively recently derived from the rest of the Australian, arid-adapted agamids.
Moloch horridus is named for the terrible Canaanite god called Moloch and horridus, meaning thorny or dreadful. They are so named because of their bizarre and imposing appearance.
Thorny devils are preyed on by Australian bustards (Ardeotis australis), humans (Homo sapiens), black-breasted buzzards (Hamirostra melanosternon) and goannas (Varanus), although they are protected from predation by their extremely armored bodies and camouflaged coloration. Thorny devils have numerous thorny spines along their bodies, including a prominent spiny "false head" on the top of their skull. When threatened by a predator they tuck their head between their forelegs and present the "false head," making it difficult for anything to swallow them. Their cryptic coloration and elaborate spiny decoration make thorny lizards difficult to see, especially when they remain motionless. They move with slow, jerky movements and will freeze when approached by a threat, often in mid-step. They will also puff themselves up with air when threatened, making themselves more difficult to handle. Other possible predators include snakes and introduced dingos (Canis lupus familiaris) and red foxes (Vulpes vulpes).
Known Predators:
Anti-predator Adaptations: cryptic
Thorny devils are well-known for the many, large spines on their bodies. Their large spines are entirely boneless, only two parietal spines are supported by modest bony bosses on the skull. Their bodies are covered with thick shields and spiny cones and they are marked with golden and brown patches that serve to camouflage them in their arid habitats. They are extremely difficult to find because of their camouflage and escape detection even at close quarters and with experts who are actively looking for them. The head is ornamented with a large, spiny boss on the back and the eyes are small. Even the ventral surface is covered in conical, non-overlapping scales. It was long assumed that the spiny armor of thorny devils was exclusively a defensive trait, protecting them from predators. However, the complicated surface texture of thorny devils also helps them to retain and absorb water through body contact, especially condensation of water on body surfaces. Thorny devil skin color varies with temperature; individuals are brown or olive in the mornings and become light yellow as temperatures rise in the afternoon. Observations suggest thorny devils use postural changes to regulate body temperature, either maximizing contact with a warm surface (the ground) or minimizing it via standing with two feet against a shrub.
Females are larger than males, averaging 45.5 g (range 33 to 88.7 g) and 91 mm snout-vent length (range 80 to 110 mm). Males average 31.2 g and 78.7 mm snout-vent length and never weigh more than 49 g or measure more than 96 mm. Body weight changes substantially throughout the year and can vary quickly, losing or gaining up to 30% of their body mass in a few months. Oviposition in females results in a substantial loss of body mass, which can be regained quickly - in one case a female gained 40% of her body mass in a little over a month.
Thorny devils have been widely compared with Phrynosoma species, North American horned lizards. Thorny devils and Phrynosoma species are an example of convergent evolution towards a highly armored, slow-moving, thermally labile, ant-specialist lizard niche.
Unlike most Australian agamids, thorny devils have no femoral pores on the ventral surface of their thighs. They also lack a supratemporal bone. There are 21 presacral vertebrae and 22 postsacral vertebrae. Thorny devils have short digits and vary in the number of phalangeal bones, with a reduced formula throughout most of their range. The primitive agamid phalangeal formula is found in portions of the range.
Thorny devil teeth are modified for their ant specialist diet. Ants are relatively hard-bodied insects, with high levels of chitin. The mandibular teeth are modified to fit neatly between two maxillary teeth, creating a shearing apparatus. Thorny devils have also lost the anterior pleurodont teeth, reflecting their use of the tongue to capture prey, rather than the teeth.
Range mass: 28.5 to 57 g.
Range length: 76 to 110 mm.
Other Physical Features: heterothermic
Sexual Dimorphism: female larger
Thorny devils live from 6 to 20 years in the wild.
Typical lifespan
Status: wild: 20 (high) years.
Average lifespan
Status: wild: 6 years.
Thorny devils are found in sand plain and sand ridge deserts and in mallee scrub on sandy soils. They are found only in sandy or sandy loam soils, not in rocky or hard soils. Vegetation in these habitats is characterized by spinifex grasses (Triodea) and acacia scrub ("mulga").
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: desert or dune
Thorny devils, or mountain devils, are found in the Great Sandy Desert interior of Australia in regions with sandy soils.
Biogeographic Regions: australian (Native )
Thorny devils are obligate myrmecophages; they eat only ants. They primarily eat ants of the genera Iridomyrmex (especially Iridiomyrmex rufoniger) and Crematogaster. Other ants recorded in their diet include Ectatomma, Monomorium, Camponotus, Pheidole, and Polyrhachis species. They are "sit-and-wait" predators, finding a feeding site near cover and waiting for their ant prey to pass. Iridomyrmex species are eaten as they pass in terrestrial trails and Crematogaster species are eaten mainly from their trails on currant bushes (Leptomeria preissiana). Thorny devils select feedings sites near Triodia tussocks or Thryptomeme or Leptomeria shrubs and only actively feed at temperatures above 24 degrees Celsius. In some areas thorny devils were only observed feeding in the morning (before 11 a.m.) or in the late afternoon (3 to 6 p.m.), but not from 11 a.m. to 3 p.m. Because ants contain chitin and formic acid and are relatively low in nutritive value, large amounts must be consumed. Thorny devils have large stomachs to accommodate consuming large numbers of ant prey; it is estimated that they eat 750 ants daily. Feeding rates averaged 2.9 ants per minute, but rates up to 1 ant per second were recorded. Research suggests that thorny devils assimilate about 59% of the metabolizable energy in their ant prey. This compares to an assimilation rate of about 70% for generalized insect diets. Their fecal pellets are distinctive: oval, black, and glossy, they easily crumble to reveal many ant exoskeletons.
Thorny devils can employ their complicated surface textures to direct water to their mouths for drinking. The base of each spine is surrounded by a deep interscalar groove that effectively collects water and these grooves interconnect to enable capillary movement of water along the body, even against the pull of gravity, as on the legs. These grooves continue onto the head and empty into the angle of the mouth for drinking. These lizards live in extremely arid regions and water condensation onto their bodies may be the most reliable and abundant form of water typically encountered.
Animal Foods: insects
Primary Diet: carnivore (Insectivore )
Thorny devils are ant-specialists and impact ant populations in the regions they inhabit. They co-occur with other insectivorous agamid lizards, including Ctenophorus isolepis and Ctenophorus inermis. However, these lizards eat a more generalized insect diet.
Thorny devils are usually heavily parasitized by nematode worms (Parapharyngodon kartana and Abbreviata species). These worms may use ants or termites as intermediate hosts to get to their lizard definitive hosts. A new species of tapeworm (Oochoristica piankai) was described from the guts of thorny devils.
Commensal/Parasitic Species:
Thorny devils are popular in zoos because of their extreme morphology. They are a unique example of adaptation to specialized diets in a harsh landscape.
Positive Impacts: research and education
There are no adverse impacts of thorny devils on humans.
Male and female thorny devils hatch out of eggs at approximately the same size and grow at similar rates for their first year. Females begin to grow faster after that and growth continues until they reach 5 years old.
Thorny devils have not been evaluated by the IUCN red list and are not listed in the CITES appendices.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Pianka et al. (1998) suggested that thorny devils may use landmarks to navigate visually.
Perception Channels: visual ; tactile ; vibrations
There is not much information on the mating system in Moloch horridus. Anecdotal evidence, as well as their wide-ranging habits during the mating season, suggests thorny devils may walk relatively long distances to converge at landmarks for mating. Limited observations suggest males approach females, bob their heads, and mount the female if she seems receptive. Females fall and roll to throw off males if they are unreceptive.
Thorny devils mate and lay eggs mainly in the late winter through early summer (August to December). Mating has also been observed in the fall, suggesting there may be a mechanism for sperm storage. Females lay eggs in oviposition burrows up to 15 cm long at depths up to 22 cm below the surface. These burrows are different from their normal burrows and are often dug into southern facing sand ridges. Females lay from 3 to 10 (median 8) eggs that are incubated for 90 to 132 days (mean 118). After laying eggs, females fill in the oviposition burrows and smooth out the surface to cover evidence of their activity. Hatchlings weigh 1.8 grams on average and measure 63 to 65 mm snout to vent length. Young apparently eat their own egg casing before climbing out of the ovipostion nest.
Breeding interval: Thorny devils breed once yearly.
Breeding season: Thorny devils mate and lay eggs mainly in the late winter through early summer (August to December).
Range number of offspring: 3 to 10.
Range gestation period: 90 to 132 days.
Average gestation period: 118 days.
Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; oviparous
Female thorny devils have fat stores that vary seasonally, with lower fat body reserves in summer and more in winter. This is related to the timing of oviposition, when they must mobilize fat reserves to supply eggs with nutrients. Three females lost from 37 to 42% of their body weight during oviposition.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female)
The thorny devil (Moloch horridus), also known commonly as the mountain devil, thorny lizard, thorny dragon, and moloch, is a species of lizard in the family Agamidae. The species is endemic to Australia. It is the sole species in the genus Moloch. It grows up to 21 cm (8.3 in) in total length (including tail), with females generally larger than males.
The thorny devil was first described by the biologist John Edward Gray in 1841. While it is the only species contained in the genus Moloch, many taxonomists suspect another species might remain to be found in the wild.[2] The thorny devil is only distantly related to the morphologically similar North American horned lizards of the genus Phrynosoma. This similarity is usually thought of as an example of convergent evolution.
The names given to this lizard reflect its appearance: the two large horned scales on its head complete the illusion of a dragon or devil. The name Moloch was used for a deity of the ancient Near East, usually depicted as a hideous beast.[3] The thorny devil also has other nicknames people have given it such as the "devil lizard", "horned lizard", and the "thorny toad".[4]
The thorny devil grows up to 21 cm (8.3 in) in total length (including tail),[5] and can live for 15 to 20 years. The females are larger than the males. Most specimens are coloured in camouflaging shades of desert browns and tans. These colours change from pale colours during warm weather to darker colours during cold weather. The thorny devil is covered entirely with conical spines that are mostly uncalcified.
An intimidating array of spikes covers the entire upper side of the body of the thorny devil. These thorny scales also help to defend it from predators. Camouflage and deception may also be used to evade predation. This lizard's unusual gait involves freezing and rocking as it moves about slowly in search of food, water, and mates.[2]
The thorny devil also features a spiny "false head" on the back of its neck, and the lizard presents this to potential predators by dipping its real head. The "false head" is made of soft tissue.[6]
The thorny devil's scales are ridged, enabling the animal to collect water by simply touching it with any part of the body, usually the limbs; capillary action transports the water to the mouth through channels in its skin.[2] The thorny devil is also equipped to harvest moisture in the dry desert following nighttime's extremely low temperatures and the subsequent condensation of dew. The process involves moisture contact, their hydrophilic skin surface structures with capillaries, and an internal transport mechanism.[7]
The same hydrophilic moisture-harvesting physiology is characteristic in the Texas horned lizard (Phrynosoma cornutum), roundtail horned lizard (Phrynosoma modestum), desert horned lizard (Phrynosoma platyrhinos), Arabian toad-headed agama (Phrynocephalus arabicus), sunwatcher toadhead agama (Phrynocephalus helioscopus), Phrynocephalus horvathi, yellow-spotted agama (Trapelus flavimaculatus), Trapelus pallidus and desert agama (Trapelus mutabilis).[8]
The thorny devil usually lives in the arid scrubland and desert that covers most of central Australia, sandplain and sandridge desert in the deep interior and the mallee belt.
The habitat of the thorny devil coincides more with the regions of sandy loam soils than with a particular climate in Western Australia.[9]
The thorny devil is covered in hard, rather sharp spines that dissuade attacks by predators by making it difficult to swallow. It also has a false head on its back. When it feels threatened by other animals, it lowers its head between its front legs, and then presents its false head. Predators that consume the thorny devil include wild birds and goannas.
The thorny devil mainly subsists on ants, especially Ochetellus flavipes and other species in the Camponotus, Ectatomma,[10] Iridomyrmex (especially Iridomyrmex rufoniger),[10] Monomorium,[10] Ochetellus, Pheidole, or Polyrhachis[10] genera.[11] Thorny devils often eat thousands of ants in one day.[2]
The thorny devil collects moisture in the dry desert by the condensation of dew. This dew forms on its skin in the early morning as it begins to warm outside. Then the dew is channeled to its mouth by gravity and capillary action via the channels between its spines. During rainfalls, capillary action allows the thorny devil to absorb water from all over its body. Capillary action also allows the thorny devil to absorb water from damp sand. Absorption through sand is the thorny devil's main source of water intake.[12]
The female thorny devil lays a clutch of three to ten eggs between September and December. She puts these in a nesting burrow about 30 cm underground. The eggs hatch after about three to four months.[13]
The popular appeal of the thorny devil is the basis of an anecdotal petty scam. American servicemen stationed in Southwest Australia decades ago (such as during World War II) were supposedly sold the thorny fruits of a species of weeds, the so-called "double gee" (Emex australis), but those were called "thorny devil eggs" as a part of the scam. Thorny devils have been kept in captivity.[2]
The thorny devil (Moloch horridus), also known commonly as the mountain devil, thorny lizard, thorny dragon, and moloch, is a species of lizard in the family Agamidae. The species is endemic to Australia. It is the sole species in the genus Moloch. It grows up to 21 cm (8.3 in) in total length (including tail), with females generally larger than males.
