Chameleons' Tongues Give Up Their Secret
New Scientist, October 21, 2000
How do chameleons manage to grab big creatures like birds using just their tongues? A Belgian scientist has come up with the answer: chameleons suck.
Many reptiles use their tongues to capture prey, and most rely on their tongue's rough surface and sticky coating of mucus to get a good grip on a target. But this only works for small prey such as insects.
Chameleons are known to feed on larger animals such as lizards and birds. But to catch animals of this size, they would need an unfeasibly big tongue with a huge surface. "It's going to be so big, it's going to be bigger than their head," says Anthony Herrel at the University of Antwerp. "It made us think there's something weird going on here."
To find out the chameleon's secret, Herrel collaborated with researchers at Northern Arizona University in Flagstaff to film them feeding. Head-on shots taken using high-speed video cameras showed the tongue changing shape just before making contact with the prey.
"A couple of milliseconds before the tongue hits, the end forms a kind of suction pad. It looks like a bit like a baseball glove," says Herrel. Subsequent frames from Herrel's video showed that once the suction cup had stuck to the prey, muscles in the tongue contracted to draw the cup back, increasing the suction.
To check his finding, Herrel anaesthetised chameleons and cut the nerves to the muscles used to form the suction cup. When these chameleons then tried to feed, their tongues simply knocked the prey out of the way instead of grabbing it.
Kurt Schwenk, an evolutionary biologist who studies reptile tongues at the University of Connecticut in Storrs, is impressed by the unusual trick. He wants to check out whether any other lizards use a similar "flick 'n' suck" technique.
Further reading: The Journal of Experimental Biology, Vol 203, p 3255.
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