STEPHEN DALTON/MINDEN PICTURES

STANDARDS

NGSS: Core Idea: LS1.A

CCSS: Literacy in Science: 8

TEKS: 6.12E, 7.11B, 7.10B, 1.6C


The Chameleon's Secret Weapon

A coating of gluey saliva helps chameleons’ tongues stick to prey

ESSENTIAL QUESTION: What are some adaptations that help animals hunt?

An insect buzzes through the air, unaware of a chameleon perching motionless nearby. In the blink of an eye, the lizard lashes out its lengthy tongue. It snags the bug mid-flight and yanks it into its mouth. Just how the lizard’s tongue holds on to prey has long been a mystery. Now scientists think they’ve discovered the chameleon’s secret: super-sticky spit.

Chameleons’ saliva has a high viscosity, or resistance to flow. That resistance makes it sticky, like honey. A chameleon needs only a thin layer of this substance coating the tip of its tongue to catch its prey, says Pascal Damman, a physicist at the University of Mons in Belgium.

Damman was part of the team of researchers who recently discovered the sticky science behind chameleons’ spit. It’s one of the many adaptations that make these animals such great hunters (see Built to Hunt). “They are probably the ultimate predators,” says Damman.

An insect buzzes through the air. It doesn’t see a chameleon perching motionless nearby. In the blink of an eye, the lizard shoots out its long tongue. It snags the bug mid-flight and yanks it into its mouth. Just how does the lizard’s tongue hold on to prey? Scientists think they’ve found the secret: super-sticky spit.

Chameleons’ saliva has a high viscosity, or resistance to flow. That makes it sticky, like honey. A thin layer of this substance coats the tip of a chameleon’s tongue. That’s all the lizard needs to catch its prey, says Pascal Damman, a physicist at the University of Mons in Belgium.

Damman was part of a team working on the mystery. They recently discovered the sticky science behind chameleons’ spit. It’s one of the many adaptations that make them great hunters (see Built to Hunt). “They are probably the ultimate predators,” says Damman.

STICKY MYSTERY

Insects make up most of a chameleon’s diet. But the lizards can also capture prey that’s up to one-third of their body size. The largest chameleons even catch small birds with their tongues. That would be like you lifting a 23 kilogram (50 pound) hamburger with your tongue.

Damman had never before done direct research on animals. Then a biologist came by his lab to ask for his thoughts on a question that had him stumped: How do chameleons’ tongues grasp prey to pull it into their mouths? 

Chameleons don’t wrap their tongues around the food they catch. Some researchers thought the lizards’ tongues used suction. Another theory was that the chameleons’ tongues had a rough surface that allowed them to make a Velcro-like bond with their meals. 

Together, the physicist and the biologist were able to look at the question with a fresh perspective. “Scientists are often blocked into their small area of research,” says Damman. He immediately thought the mechanism must be some sticky substance on chameleons’ tongues.  

Insects make up most of a chameleon’s diet. But the lizards can also capture larger prey. They nab creatures that are up to one-third of their body size. The largest chameleons even catch small birds with their tongues. That would be like you lifting a 23 kilogram (50 pound) hamburger with your tongue.

Damman had never studied animals directly before. Then a biologist came by his lab. He wanted Damman’s thoughts on a question that had him stumped: How do chameleons’ tongues grasp prey to pull it into their mouths? 

Chameleons don’t wrap their tongues around the food they catch. Some researchers thought the lizards’ tongues used suction. Another idea involved the tongues’ rough surface. Maybe this allowed their tongues to stick to their meals, like Velcro. 

The physicist and the biologist looked at the question together. This helped them to see it from a fresh angle. “Scientists are often blocked into their small area of research,” says Damman. Right away, he thought the answer must be some sticky substance on chameleons’ tongues.  

SALIVA TEST

To test the question, the research team collected a small amount of chameleon saliva on a glass plate. They tilted the plate and rolled a small steel ball across it to measure how well the saliva slowed the ball. 

The chameleon saliva was stickiest when the ball moved quickly. That means when a chameleon’s tongue shoots out at lightning speeds, its force of adhesion—attraction between unlike substances—increases. When the tongue stops moving, the bond with its prey loosens. Otherwise, chameleons wouldn’t be able to eat their prey without biting their own tongues. 

After spending two years tackling the biology mystery, Damman is ready to explore another one. He’s now investigating how bees’ tongues capture viscous nectar from flowers. “It’s always interesting to start a new project,” says Damman. “You have to get outside your comfort zone.”

The team needed to test the question. So they placed a small amount of chameleon saliva on a glass plate. They tilted the plate and rolled a small steel ball across it. As the ball moved, they measured how well the saliva slowed it. 

The saliva was stickiest when the ball moved quickly. That revealed what happens when a chameleon’s tongue shoots out at lightning speeds. Its force of adhesion—attraction between unlike substances—increases. When the tongue stops moving, the bond loosens. If it didn’t, the lizards wouldn’t be able to eat their prey without biting their own tongues. 

Damman spent two years tackling the biology mystery. Now he’s ready to explore another one. He’s studying how bees’ tongues capture gooey nectar from flowers. “It’s always interesting to start a new project,” says Damman. “You have to get outside your comfort zone.”

CORE QUESTION: How did scientists discover how chameleons' tongues help catch prey?

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