Oct. 17, 2000
The secret behind the sticky thwop of a chameleon's tongue
as it sticks and grips its prey is finally out: the tongue
fastens itself to victims with suction, an international team
of biologists says.
Squeezing a slippery knob in the throat, a chameleon
tongue launches itself at targets up to two body lengths away,
then retracts with its quarry like an accordion.
But Belgian biologist Anthony Herrel says it was not these
ballistics that startled him. After having studied how other
lizards feed for eight years, he saw a chameleon lasso a
lizard nearly the same size as itself.
"They're not supposed to do that," says Herrel.
The tongues aren't big enough or sticky enough to bag such
big game with simple adhesion, he says.
An idea raised in 1983 by evolutionary biologist Kurt
Schwenk suggested an explanation. Schwenk had described the
muscles beneath the tip of a chameleon's tongue, which forms a
flat pad at rest, but in flight, dimples into a deep, conical
mitt that engulfs the target.
With these muscles the mitt might act like a suction cup,
Schwenk hypothesized, and achieve a seal with the tongue's
In the current issue of the Journal of Experimental
Biology, Herrel and colleagues describe testing the idea
by shaping the flaccid tongue pouches of anaesthetized
chameleons around a straw that was either sealed or open at
both ends. They then electrically stimulated the muscles to
Around the sealed straw the pouch was airtight, but the
open straw allowed air to enter. With a tug on the straw, the
researchers assessed the tongues' grip. They clung with
two-and-a-half times the force to the sealed straw.
"It's a beautiful paper," says Schwenk, who now teaches at
the University of Connecticut in Storrs.
Additional tests included recording muscle contractions
from dangling wires in awake chameleons as their tongues
hurled through the air, as well as X-ray and high-speed
movies. Herrel and colleagues put ten species of chameleons
from Africa and Madagascar through the tests, and conclude
they're all doing the same thing.
Herrel says chameleons' iron grips support their sedentary
lifestyle. It means they can bag pretty much whatever walks or
flies in range.
"That's pretty important if you're not going to move much,"