(Credit: Svoboda Pavel/Shutterstock) Chameleons present an intriguing puzzle for biologists. From their bulging eyes to their color-swapping skin, they possess a host of unique adaptions. Now, another piece of their mysterious physiology has come to light. Researchers from France and Belgium have discovered how chameleons hang on to their prey once they’ve snatched it with their tongues. A chameleon’s tongue can be up to twice its body length — over two feet in some cases — and operates something like an arrow fired from a bow. Using elastic tissues, chameleons launch their tongues toward prey at accelerations of up to 20 feet per second. If judged perfectly, their tongue grabs unfortunate insects or small lizards at the apex of the shot and drags it into their mouth.
The Key Is Spit
The firing mechanism is well understood, but how they hold on to their prey even at accelerations of around 40 g’s was not. In a new experiment, the researchers show that a chameleon’s firm grip actually comes down to a simple physical property of their spit. Chameleon saliva is a whopping 400 times thicker than ours, they say, which enables viscous adhesion — the ability of thick liquids to hold two surfaces together when pressed between them. The researchers tested the viscosity of chameleon saliva by holding a glass plate in front of a tasty-looking insect. When the chameleon flicked its tongue outward, it hit the glass, leaving a thin layer of spit behind. The researchers then tested how thick it was by rolling beads down the glass and comparing their speed to plates covered in other substances whose viscosities were known. They published their research Monday in the journal Nature Physics. They say that the thickness of chameleon saliva alone is enough to account for their gripping power. Previous hypotheses held that their tongues employed suction cups or a Velcro-like hold to help grab onto prey. Instead it seems that all they need is some really thick spit.
In addition to being covered with thick mucus, chameleons’ tongues are wider at the tip, increasing the surface area available for gripping and the strength of the hold. Chameleons have been known to consume prey that weigh up to 30 percent of their body mass, something they accomplish almost completely through the use of their saliva. While the researchers equations predicted that they should be able to handle even larger prey, factors such as slightly off-target tongue attacks may decrease that number. Our own tongues would be of little use as hunting weapons, even if we were able to shoot them like fleshy harpoons. With human saliva, the researchers say that chameleons would have to hunt prey 50 times smaller than they currently do. Our saliva is just too thin for the job — a chameleon’s spit is closer in consistency to honey.