Tuesday, 10 June 2014

Australia's thorny dragon

Image of a Thorny dragon (Moloch horridus)
Thorny dragon
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Family: Agamidae
Genus: Moloch
Species: Moloch horridus
Conservation Status: Not yet assessed
Common name(s): Thorny dragon, thorny lizard, thorny devil, mountain devil and moloch

The thorny dragon is a small, scary-looking species of lizard occurring exclusively in Australia and is the sole species of the genus Moloch. It's a truly bizarre creature, with no other lizard in the world coming remotely close to it.

One of the species most strange features is how it consumes water, with its skin acting as blotting paper, sucking the water from the ground and directing it upwards, until it reaches its mouth! Another unique feature is its fake head. When threatened, the thorny dragon burrows its real head, leaving the pretend, thorn-covered, head exposed.

Now, let's see this weird little creature in more detail.

Habitat & Distribution
The species is found throughout the arid regions of Western Australia, the Northern Territory, south-western Queensland and western South Australia. It occurs in sand, spinifex grasslands and scrub and is a very common sight throughout the Shark Bay World Heritage Area. Their distribution coincides mostly with the regions of sandy loam soils than with a particular climate in Western Australia .Vegetation in their habitats is primarily composed of spinifex grasses (Triodea) and acacia scrub (mulga).

Image showing the distribution of the thorny dragon
Thorny dragon distribution

Thorny dragons reach a maximum length of about 20 cm (~7.8 in), with females being slightly larger and paler than males. Females have an average weight of 45.5 g and an average snout-to-vent length of 9.1 cm whereas males have an average weight of 31.2 g and a snout-to-vent length of 7.87 cm. The body weight of females changes substantially throughout the breeding period, as they gain or lose up to 30% of their body mass.

The body is marked with yellow, orange, brown and white markings and is covered by cone shaped, usually non-calcified spines. The spines are hard and sharp, making the animal difficult to swallow. There are also two relatively large spines, one above each eye. This is why the animal is also known as the thorny devil.

Depending on the soil, surroundings, temperature and amount of sunlight, the thorny dragon can change its color from yellow to reddish brown to black, allowing it to blend in with the environment. Camouflaging and pointy spikes are two great defensive mechanisms that protect it from potential predators. However, this creature has one more ace up its sleeve. It has a fake, spiny and knob-like head, right behind its real head.

When threatened, the lizard will dip its real head down. There isn't much research on this, but it is presumed that this method is effective against pecking predators, like birds.

Its maximum lifespan in the wild is at least twenty years, and individuals reach sexual maturity at three years of age.

Before going to sleep, they dig up the soil and cover themselves with it. This allows them to stay warmer during the cold nights. During the day, they protect themselves by staying in their underground burrows, which are commonly found under scrub that provides extra protection from the heat.

Video about the thorny dragon by National Geographic

This strange animal is an obligate myrmecophagous, meaning that it solely feeds on ants, typically species of the genera Iridomyrmex and Crematogaster. They have also been recorded to eat ants of the genera Ectatomma,Monomorium, Camponotus, Pheidole, and Polyrhachis.

They are not active predators. They simply find a good "spot" and use their tongue to eat passing ants. Since ants are nutritionally poor, the thorny devil needs to eat lots and lots of them. Estimations give an average of at least 750 ants per day, although they can easily eat a thousand. Research suggests an average feeding rate of about 3 ants per minute, but rates of up to an ant per second are possible if they hit a really good "spot".

The species has been observed feeding in the morning (before 11:00) or in the late afternoon (15:00 to 18:00), but never from 11:00 to 15:00.

Thorny Dragon - Notice the pseudo-head

Thorny devils are known to be preyed by:
  • Australian bustards (Ardeotis australis - a large ground bird) 
  • Black-breasted buzzards (Hamirostra melanosternon - a large eagle-like bird ) 
  • Sand goannas (Varanus gouldii - a large monitor lizard) 
  • Black-headed monitor (Varanus tristis - a large monitor lizard ) 

Other possible but not recorded predators include snakes, dogs and red foxes.

As aforementioned, thorny scales, camouflage and deception using their pseudo-head are the species' main means of protection. The species can also swallow air to puff up, making it even more difficult to handle and swallow. Finally, when threatened, it can lock its spine and curved tail down the ground, deterring predators from flipping it over.

Image of a thorny dragon somewhere at the Great Central Road (WA)
Thorny devil at the Great Central Road 

Coping with Water Scarcity
Lack of water creates a survival problem for all desert plants and animals and like most of them, the thorny dragon has come up with a really nifty trick to collect water. The thorny dragon's skin is ridged, and acts as blotting paper, sucking and directing the water to the mouth for drinking. How this happens?

Each spine is surrounded by a deep interscalar groove that collects water. These grooves are all interconnected and enable capillary movement of water from any part of the body, including the legs. The grooves eventually lead to the head and empty into the mouth. This allows the lizard to collect water from the morning dew and from damp sand

Excerpt from a BBC documentary
At 2:25 you can see a Thorny dragon eating ants.
At 3:52 you can see the lizard's unique method for collecting water.

Not much is known about the lizard's mating system. Anecdotal evidence and observations suggest that individuals walk relatively long distances, to converge at landmarks for mating. It seems that males approach females, bob their heads, and try to mount them. If the female is receptive the two will mate, otherwise she will fall and roll to throw off the male. Mating occurs once every year.

Females lay their eggs from August to December. The eggs are laid in burrows up to 15 cm (~6 in.) long, at depths up to 22 cm (8.5 in) below the surface. These burrows are different from the normal burrows they use to rest and are typically made into southern facing sand ridges. Gestation lasts 90 to 132 days.

Females lay 3 to 10 (median 8) eggs and the incubation period lasts 90 to 132 days (median 118). Mothers than fill their burrows and smooth out the surface to cover any evidence. The average weight for hatchlings is 1.8 grams and their snout-to-vent length is 6.3 to 6.5 cm. The youngs probably eat their own eggs until they are strong enough to climb out the burrow.

Conservation Status & Threats
Thorny devils have not been evaluated by the IUCN. Due to the species wide distribution and relative abundance they are presumed to not be immediately threatened.

Image of a Thorny devil, somewhere in South Australia
Thorny devil, somewhere in South Australia

In captivity
Thorny devils are a popular attraction in Australian zoos, mainly because of their strange appearance. In 2013, Adam Sapiano, a reptile breeder and storeowner in Victoria, Australia became the first private breeder that received permission to breed this unique animal.

Is it dangerous?
Despite its somewhat frightening appearance, the thorny devil is harmless to humans. Don't forget, it's a little, slow moving creature, that spends most of its time either eating ants or hiding its presence!

Other Interesting Facts about Thorny Dragons
- The lizard’s scientific name, Moloch horridus, was derived from "Paradise Lost", an epic poem in blank verse by the 17th-century English poet John Milton (1608-1674). In the poem, the Canaanite god Moloch is described as a "horrid king besmeared with blood of human sacrifice".
- The purpose of the two large spines on its head -if there is one- is still unknown.
- Research suggests that the spines may also be used to store fat and/or water.
- The species was first described by the British zoologist John Edward Gray (1800-1875) in 1841.
- The species is heavily parasitized by nematode worms, including many species of the genus Abbreviata and by Parapharyngodon kartana. These worms possibly use ants as intermediate hosts. In 1996, a new species of tapeworm (Oochoristica piankai) was found in the guts of thorny lizards.

Video of a thorny devil, walking slowing on the sand

You may also like
  • Short-horned Lizard: Do you think that having a second fake head is a weird way to defend yourself? Think again! The short-horned lizard shoots blood from its eyes to discourage predators!
  • Komodo Dragon: With individuals commonly reaching lengths of 2.0 m (~6.5 ft), the komodo dragon is a sight to behold. Learn more about the world's biggest lizard.

References & Further Reading
- BENTLEY PJ, & BLUMER WF (1962). Uptake of water by the lizard, Moloch horridus. Nature, 194, 699-700 PMID: 13867381
- Withers, P. (1993). Cutaneous Water Acquisition by the Thorny Devil (Moloch horridus: Agamidae) Journal of Herpetology, 27 (3) DOI: 10.2307/1565146
- Kluge, A., & Greer, A. (1991). The Biology and Evolution of Australian Lizards Copeia, 1991 (2) DOI: 10.2307/1446607
- Pianka, E., & Pianka, H. (1970). The Ecology of Moloch horridus (Lacertilia: Agamidae) in Western Australia Copeia, 1970 (1) DOI: 10.2307/1441978
- Meyers JJ, & Herrel A (2005). Prey capture kinematics of ant-eating lizards. The Journal of experimental biology, 208 (Pt 1), 113-27 PMID: 15601883
- Bursey, C. R., S. R. Goldberg, and D . N. Woolery. 1996. Oochoristica piankai sp. n. (Cestoda: Linstowiidae) and other Helminths of Moloch horridus (Sauria: Agamidae) from Australia. J. Helminthol. Soc. Was. 63: 215-221.
- Pianka, G., E. Pianka, G. Thompson. 1998. Natural history of thorny devils Moloch horridus (Lacertilia: Agamidae) in the Great Victoria Desert. Journal of the Royal Society of Western Australia, 81: 183-190.
- Pianka, E. 2009. "Australia's thorny devil" (On-line). University of Texas.
- Pianka, E. 2003. "Moloch horridus" (On-line). Digimorph. Accessed January 25, 2009 at

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