The chameleon's ballistic tongue, unravelled
Mathematicians modelled the mechanics of the lizard's super-speedy tongue flick. Belinda Smith reports.
The blisteringly quick flick of a chameleon's tongue can accelerate to 100 kilometres per hour in one hundredth of a second and extend two and a half times its body length to pluck an insect out of the air.
Now, mathematicians from the University of Oxford in the UK and Tufts University in the US have mathematically modelled the tongue's energy storage and release.
The biophysical model, published in the Proceedings of the Royal Society A, involves three distinct subsystems to the "ballistic projection": muscle mechanics, extension dynamics and the telescoping mechanism.
A chameleon tongue's firing mechanism comprises coils of accelerator muscles which launch it and the retractor muscles. At rest, these sets of muscle are wrapped around a mouth bone-like structure called the entoglossal process.
When the chameleon prepares to strike, the accelerator muscles contract, then blast off their entoglossal process launch pad.
As the accelerator muscle contracts, it squeezes tubular segments inside it called intralingual sheets. They're pushed to the end of the tongue – what the researchers called the "loaded position" – and flick out telescopically, not unlike, they write, "the popular laser saber toy from the Star Wars franchise".
Intralingual sheaths are made of collagen so are very stretchy, but also have the added benefit of storing elastic energy. As they fire, that elastic energy is converted into movement, which propels the sticky tongue tip further and faster.
Once the tongue is fully extended, retractor muscles reel it in again, along with the unfortunate prey.
By incorporating these subsystems into one mathematical model, the researchers were able to tweak various parameters, such as the radii of intralingual sheets, and see what happened to the tongue.
For instance, they found the inner sheath radius had to be less than 1.4 millimetres – any wider and it would disconnect from its bony launch pad.
Watch a chameleon in action:
Edit: this article originally claimed the chameleon tongue could reach speeds of 26 kilometres per second. This is incorrect and has been amended.