The colorful chameleon fires its long, elastic tongue at an incredibly high-speed to zap an unsuspecting prey. It is also known that their tongues don’t wrap around the insects while pulling them back. So, how does the prey remain attached to the chameleon’s tongue? Scientists at the University of Mons in Belgium found that the secret lies in their sticky saliva.
Their spit is as viscous as honey
According to a study published Tuesday in the journal Nature Physics, the chameleons’ spit is 400 times stickier than human spit. It means their spit is as viscous as honey. It was the first study to examine the viscosity of mucus from the tongues of these colorful lizards. Researchers led by Pascal Damman waited for a captive veiled chameleon Chamaeleo calyptratus throw its tongue at a clean slab of grass, behind which researchers had placed several crickets.
When they analyzed the saliva sample, they found that it was a strong enough glue to pick up even large insects. Chameleons can swallow prey up to 30% of their own body mass. Researchers believe that the size of the prey depends not on the stickiness of their saliva, but on the size of their mouth. Since chameleons swallow insects in whole, they can’t ensnare something that doesn’t fit in their mouth.
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How researchers measured the viscosity of chameleon saliva
Damman and his colleagues measured the adhesiveness of the saliva by smearing it on a slanted glass plate and then rolling a small bead down it. It allowed them to measure the viscosity of the mucus by comparing how fast the bead rolled down a decline with and without the saliva on it. Other scientists believe mucus may not be the only factory because Damman didn’t discuss the roles of surface tension and lingual suction that have been demonstrated to occur in chameleons.
The high speed at which the lizard’s tongue accelerates and retracts makes saliva even more effective. “When the tongue pulls rapidly, it makes the adhesion higher,” said Damman. But if the mucus is stressed slowly, it behaves like a liquid with little stickiness.