Science

  • Issue 121 / January - February 2018



    The Thorny Devil: A Lizard with Unusual Physical Features

    Rumeysa Yazar

    Australia is an extraordinary part of the earth, with its scorching sand mountains that stretch across barren plains, rock columns each unique and amazing, labyrinth-like domes that rise like towers, spine-chilling cliffs, misty rainforests, highlands and national parks. A land of dreams for many people, Australia is also a paradise for endemic creatures. A visit to the desert offers a chance to extend dreams beyond the horizon if the visitor happens to spot a reptile or snake rushing past from among the cracks in the red-hot rocks. This is an entirely alien place. The letters the Lord has presented for eyes to see inspire a different kind of awe of the Artist.



    One such wonder, the thorny devil (Molochhorridus), is an endemic creature that presents itself as a source of contemplation. It is a lizard between 10 and 15 cm long, with a broad body that is completely covered with cone-shaped sharp spikes, and has a rather big head and small eyes. Its appearance is made even more frightening with the two spikes on the sides of its head, which look like horns and are stronger than the others. On the back of the lizard’s head is a separate bump that resembles a second head on which there is another big spike. These unusual physical features have earned it the name the thorny devil. The lizard’s golden and brown patchy skin provides camouflage in the desert environment. Having a lifespan of between 12 and 20 years, this work of art is equipped with unique features that inspire greater awe as they are studied.



    Deterrent tactics

    Living in the harsh conditions of the desert, the thorny devil is equipped with tactics, each more interesting and unusual than the rest, to keep enemies at bay and stay clear of danger. First and foremost, the thorny devil’s color gets dull when it is frightened or cold, which adds to its melding with the environment. It also breathes in and holds the breath to enlarge its body and thus makes its already frightening appearance even more so. If the tactic does not work to deter the enemy, another strategy is put in place. The creature lowers its head until the lump with the thorn protrudes further. By producing its biggest weapon against the enemy, it seems to say “Don’t you dare come closer” and fends it off.



    Skin and feet like a sponge

    The most hidden secret of the thorny devil lies in its ability to absorb water through its skin and even feet. The thorny devil is geared up with a special skin make-up that can collect and transport water to the mouth as required by the environment. This structure is a mechanism that involves micro capillary tubes and a network of channels that connects them. The architecture of the network allows for capillary movement, that is, water can resist gravity and move upwards. This is how the lizard is enabled to drink water from sources like ponds, wet sand and droplets condensing on the skin. For example, this little desert creature can absorb water through its feet simply by standing on a little pond, without having to lower its mouth. Drinking water directly from water sources is already difficult, because the tongue and jaw structure of thorny devil is specially created to hunt its prey.



    To unravel the intricacies of this mechanism, studies were conducted in the labs of the University of Western Australia on specimens of the Molochhorridus from the Gibson Desert. The studies focused on five water sources that could feed the creature: the rainfall, puddles, moist soil, water droplets from dew, and thermally-induced condensation. The aim was to uncover the effectiveness and efficiency of these sources in the thorny devil’s moisture-harvesting.



    In the most striking of these experiments, which looked into collecting water from puddles, the lizards were placed in a puddle of 3 mm deep and the changes in their weight were measured. The thorny devils were divided into two groups as those that drank water and those that did not and were then observed for 60 minutes. It was found that there was a weight increase of 3.66 percent in the lizards with no jaw movement (i.e. non-drinking lizards). On the other hand, the increase in weight was found to be significantly higher at 6.84 percent for the lizards which had rhythmical jaw movements (i.e. drinking lizards). An examination of the jaw movements showed that every jaw movement accounted for the absorption of 0.7 milliliters of water.

    To measure the lizards’ absorption of water from “moist sand” they were placed on soil containing different levels of water, varying between 3 to 22 percent. The amount of water absorbed through feet and skin was measured through differences in weight. It was found that water absorption increased proportionately as water content increased. A weight increase of 0.20 percent was found even in soil that contained 2 percent water; in soil with water content of 22 percent, the creature’s water collection amount averaged 1.84 percent. Although little, the increase was concluded to be significant.



    Moreover, experiments with “pre-heating with moist sand” showed that pre-heating had a significant impact on the ability of the skin to draw water. It was also found that water collection through “water condensation supported by difference in heat and moisture” caused a weight gain increase of 0.215 percent. These studies show how fantastic a capillary system the thorny devil is equipped with to collect water from different sources, and thereby quench its thirst.

    When we lend an ear to this little but amazing creature, we can almost hear it say that every living thing in the nature is being duly taken care of.


    Surely God it is He Who is the All-Providing, Lord of all might, and the All-Forceful.

    (Qur’an 51:58)

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