Chameleons are vicious little predators. They hunt bugs, birds, mice, and even other chameleons using only one weapon: their tongues. New research shows precisely how good these weapons are: the tip of a chameleon’s tongue produces a mucus that’s 400 times more sticky than human saliva, allowing the hungry reptile to catch prey up to a third of its body weight.
A chameleon's weapon is its tongue
Their hunting strategy is ingenious: chameleons just wait motionless until a harmless grasshopper or a locust walks by. When they sense prey, chameleons shoot out their projectile tongues, which can extend to twice the length of their bodies, and catch their dinner. Today’s study is the first to explain exactly how these slimy tongues work so effectively.
To find out, the researchers collected a saliva sample from the most common type of chameleon, Chamaeleo calyptratus. To do this, they placed small crickets behind a glass pane and waited for the chameleon to shoot its tongue out. When the tongue hit the glass, it left behind a smear of saliva, which the researchers then collected. "It was very easy," says study co-author Pascal Damman, of Université de Mons in Belgium.
The next task was to determine just how viscous the chameleon spit was. They rolled a bead on a tilted plate — which had been doused in the saliva. That let them measure how much the saliva’s stickiness slowed the bead’s descent, therefore allowing them to calculate the spit’s viscosity.
Chameleon saliva, it turns out, is about as sticky as honey. This allows the chameleon to keep hold of its prey even as its projectile tongue quickly retracts back into the mouth, with an acceleration of 40 Gs. (For comparison, a military fighter jet can have acceleration forces as high a 9 Gs.) Another impressive feature the researchers found has to do with the shape of the tongue. When the tip touches its prey, it forms a sort of cup that envelops the prey, making capture easier.
But the stickiness of the spit was what surprised scientists the most. Damman described the finding as "completely unexpected." The same sticky saliva properties probably also apply to other animals like salamanders, toads, and frogs that use their tongues to fetch their meals, the researchers wrote in the study, published in the journal Nature Physics.