Issue 2

In the process of trying to write this article, I have spent far longer than I care to admit chasing a rather loud, annoying fly around the room in which I am currently working.  Surprise to say I have yet to succeed in catching it. The only small consolation I can take from my undeniable failure is that at least my dinner doesn’t depend on my success. The story is, however, very different for the chameleon. There are approximately 160 species of chameleon, almost half of which can be found living on the island of Madagascar. They come in a huge range of shapes and sizes, from the male Furcifer oustaleti (leading the way at 63.5cm) to the Brookesia micra, which can reach a maximum size of just 29mm! And with most of these fascinating creatures being arboreal, it begs the age old questions of ‘what’s for dinner?’ and ‘how do I catch it?’

As I have previously demonstrated, catching insects is not always easy. They are fast, agile, and even at rest often very well camouflaged. But fortunately evolution has not left the chameleon completely unaided. It’s a well-known fact that chameleons are the proud owners of perhaps the most amazing tongue in the animal kingdom. A chameleons tongue can be between 1.5 to 2 times the length of its own body (excluding the tail), although scientists currently believing the ratio to be even greater in smaller species.

The base of this amazing evolutionary feature is the ‘U’ shaped hyoid bone at the back of the chameleon’s mouth. Attached to the centre of this bone is the hyoid horn, a tapering cartilaginous spike that sits inside the hollow tongue.  The tongue itself consist of three main parts, the stick tip used to suction prey, the accelerator muscles used to propel the tongue the towards its unlucky victim, and the retractor muscles, which pretty much do what they says on the tin.

The accelerator muscles consist of muscular rings than squeeze against the central hyoid horn. Due to its tapered shape, this forces the tongue forward and out of the mouth. Between the muscle and the horn are lubricated cavities that reduce friction and allow the tongue to travel at speeds of up to 20km an hour! The lizard can then vary the length of the strike by using a tendon attached to the tip of the hyoid horn, stopping the tongue mid-flight. At the tip of the tongue is a bulbous ball of muscle covered in an adhesive saliva, that rapidly forms a small suction cup around the prey upon impact. Although most targets will now be well and truly stuck, slimy insects such as worms and slugs present difficultly for the chameleon because the saliva won’t stick to their wet surfaces.

The final challenge the chameleon must face is withdrawing its tongue, and hopefully its dinner, back into its mouth. Retractor muscles fold around the hyoid horn and stretch when the tongue is realised. They then contract, bringing the tongue back into its resting position at the bottom of the mouth. Because there is less urgency, the retractor muscles don’t exhibit the same speed as the accelerator muscles, although they are capable of pulling a weight equal to half the chameleon’s body!

While the mechanics behind this amazing feat seem pretty simply, the results are devastatingly effective. But how do these sharp shots know where to aim? The key to their success is their distinctive eyes, which can be rotated and focused independently from one another. This gives the lizard an amazing 360° view of its surroundings. Although at first it appeared that chameleons used both their eyes to focus on prey items (stereopsis), research has shown that the angle of eye convergence is too variable to allow for triangulation. It is therefore more likely that chameleons use monocular depth perception to locate their prey. Once the prey had been sighed, the lizard will use its entire head to set its aim. The tongue is then brought forward to the front of the mouth and the hyoid bone is raised from the lower jaw, ready for action. In fact, the aim of these reptiles is so incredibly accurate that Houston (1828) observed two captive females connect tongues when a fly was placed midway between them!

Now that my own fly has finally made its way safely out of the window, I am left sat here feeling that my own tongue is very inadequate indeed! There is no denying that when it comes to tongues, that of the chameleon almost always comes up trumps!