Scientists have determined that other lizards catch prey by using mainly surface tension--the stickiness created when a wet tongue contacts dry prey. But chameleons consume creatures much too large for surface tension alone to handle. So evolutionary biologist Anthony Herrel and colleagues at the University of Antwerp in Belgium and Northern Arizona University in Flagstaff decided to find out what else is going on. Dissecting tongues from several chameleon species, they found that two muscles form a pouch at the tip. Slow-motion film of chameleons capturing crickets, grasshoppers, and other lizards revealed that these muscles retract just before the tongue makes contact with the target.

The team suspected that the tongue pouch was behaving like a suction cup. So they anesthetized chameleons, inserted a glass tube into the pouch, and measured the force required to remove the tube as the pouch muscles were electrically stimulated. It took 10 times greater force to remove a sealed tube than a hollow (nonsuctionable) tube. The team also cut the nerve that controls the pouch muscles and found that although the animals could still extend their tongues, they couldn't latch onto prey. (The nerve later healed normally, says Herrel's colleague Kiisa Nishikawa.)

Those vacuum-generating tongues may be unique, says evolutionary biologist Kurt Schwenk of the University of Connecticut, Storrs. A better understanding of this unusual mechanism, he notes, should help scientists understand how it evolved.