Zoological Investigations

They say it is better to have loved and lost than never to have loved at all, and in general, I agree. After all, Alzheimer’s aside, memories are forever, right? So let’s let the good times roll and get on with it.

You may not know why, but that brief yet significant introduction brings me to this week’s subject: the crested gecko, Rhacodactylus ciliatus. Crested geckos are endemic to New Caledonia, an island located just about halfway between Australia and New Zealand. I’ve talked about islands before, so I’ll just point out that roughly 86 per cent of New Caledonian reptiles are not found anywhere else in the world.

Originally described in 1866, the crested gecko was believed extinct until it was rediscovered by science in 1994. Since that time, and due to the relative ease with which they can be bred in captivity, crested geckos have become widely popular as pets.

Permit me, if I may, to briefly state that captive crested geckos require at least 50 per cent humidity and temperatures between 20 C and 26 C. Their enclosures should be tall enough to permit climbing; they should have things to climb on; you cannot keep mature males together and they do best with a variety of live invertebrates and fresh fruits to eat, supplemented with commercially available vitamins and calcium. Don’t let anyone tell you any different.

There are six species within the genus Rhacodactylus, all of which are found only on the island of New Caledonia. One species, the New Caledonian giant gecko, R. trachyrhynchus, is listed as endangered by the International Union for Conservation of Nature (IUCN) and is also the largest known gecko on the planet today. In gecko terms, the 34 centimetres in length R. trachyrhynchus can reach makes it a giant. In contrast, R. ciliatus, the species most often sold in stores, generally reaches lengths of around 10-26 centimetres, about half of which is tail.

Crested geckos are nocturnal, predominantly arboreal and very cute. They can be various shades of brown to grey to red, and their colour may become more or less vibrant depending on environmental conditions and the time of day. Their name derives from the fact that they have lightly spiked fringes on either side of the head, which run from the base of the eye, over the dorsal surface of the orbit (eye socket) and down towards the neck. This gives them the appearance of having long, flirtatious eyelashes, enhancing their popularity in the pet trade, but more importantly acting to deter potential predators.

Crested geckos do not have eyelashes. They have a thin, transparent layer called a nictitating membrane, which can be drawn across to protect and moisten the eye. One of my favourite things about crested geckos is that they often just sit and lick their eyeballs, especially after eating. Their tongue is very long and soft, with a widened spatula-like tip. Nothing else that can lick its own eyeball has ever looked so endearing while doing it, let me tell you.

Unlike other lizards, crested geckos have a prehensile tail, which helps them to grip branches whilst roaming about the lush rainforests of New Caledonia. In addition, their tail is flattened at the tip and equipped with minute transverse folds called lamellae. These lamellae are further divided into many tiny bristles, or setae, made of a hard organic protein called keratin. The setae get even more complex under a microscope; they are further sub-divided into minute hairs, only 200 nanometres in diameter. The broad toe pads of the crested and many other gecko species have these same features, which vastly increases surface area and enables the gecko to climb vertical and very smooth surfaces with great skill and agility. Part of this adhesive magic involves the weak van der Waals forces you may have tried to ignore in chemistry class.

Crested geckos are currently being reviewed by the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES) for classification. Only two of the six species have so far been classified, with R. auriculatus listed as least concern and R. trachyrhynchus endangered.

This article dedicated to the memory of Mr. Twist.