The rheometer the machine that measures viscosity requires about one-fifth of a teaspoon of fluid to run the test. Amphibians are unique in that they secrete saliva through glands located on their tongue. So, one night we spent a few hours scraping 15 dead frog tongues to get a saliva sample large enough for testing.
After testing, we were surprised to find that the saliva is a shear-thinning viscoelastic fluid. The saliva has two distinct regimes: high viscosity thick like honey and low viscosity 50 times less viscous. The two regimes are dependent on how quickly the saliva is sheared, when resting between parallel plates. Shear rate can be compared to rubbing fluid between your fingertips at different speeds. A common shear-thinning fluid is ketchup, which sticks to the insides of bottles but can flow when the bottle is tapped.
The soft tongue and the shear-thinning, viscoelastic saliva working in unison to adhere to insects. The extreme softness of the tongue allows it to deform and engulf the insect during prey impact. During insect retraction, the tongue acts like a spring, storing energy in the soft tissue and reducing separation forces between saliva and insect.
You can imagine the tongue acts like a bungee cord for the insect; if the tongue were stiffer, it would be like a human jumping off a bridge with a stiff rope wrapped around the ankle. The saliva has unique properties that maintain adhesion. But if you press down on it, it turns solid.
Frog saliva behaves in the opposite way. When the slobbery tongue smacks its prey, the saliva becomes more liquid and spreads into all the cracks and crevices of its prey. As the frog retracts its tongue, the saliva thickens, making it harder for the prey to separate from the tongue.
Imagine trying to pull apart fingers stuck together with peanut butter, Noel said. To figure this out, Noel had to scrape the tongues of 15 donated frozen leopard frog specimens. The fruits of her labor resulted in about one-fifth of a teaspoon of the stuff, which she ran through a device that gauges viscosity , a measure of how well a liquid flows. The researchers found that frog tongues are among the softest biological materials known to science — 10 times softer than human tongues, or about as soft as brain tissue.
This gives the tongue its stretchy quality, much like a bungee cord. As it flies back toward the mouth, it absorbs and stores much of the force that would otherwise cause the insect to separate from the tongue. The findings could aid in the development of adhesives capable of rapidly grabbing delicate items, such as microchips, off conveyor belts without damaging them. A sticky frog tongue mechanism could also be attached to a drone to capture objects in mid-air, Noel said.
That study earned an Ig Nobel Prize in Dinosaur surprise: Scientists find collagen inside a million-year-old bone. How to reset your body clock — and get better sleep — with hiking boots and a tent.
A frog's tongue is 10 times softer than ours, about as pliable as your brain, in fact. And this softness makes it super flexible so it can wrap itself around its victim, slathering the fly with a super sticky saliva, trapping it in place like glue. This fly is going nowhere. All that's left to do is reel it in. The frog's retractor muscle yanks on the tongue, which zooms backwards like a bungee cord. To dislodge its prize, the frog sucks its eyeballs back into its head.
That pressure slides the prey off its tongue, ready to be swallowed whole. World globe An icon of the world globe, indicating different international options. Get the Insider App. Click here to learn more. A leading-edge research firm focused on digital transformation. Good Subscriber Account active since Shortcuts. Account icon An icon in the shape of a person's head and shoulders.
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