What was the inspiration for looking at what makes frogs good at catching prey?
Inspiration came from two places: the amphibian collection at the Atlanta Botanical Gardens (now the Amphibian Foundation, Inc.) and a Youtube video. We had been speaking with lead herpetologist Mark Mandica (co-author of the paper) about unique frog characteristics, when we ran across this very silly video of a frog attempting to eat fake ants off a phone screen (https://www.youtube.com/watch?v=WlEzvdlYRes). While everyone knew that the frog tongue is sticky, no one had yet to figure out just how the tongue captured insects so quickly.
You state that “the tongue is highly damped like a car’s shock absorber”. Could you explain a little bit more what you mean by that/ how that helps?
The viscoelastic properties of the tongue aid in reducing the separation force between saliva and insect during retraction. By utilizing both elastic and damping mechanisms within the tongue tissue, the frog is able to maintain high contact with its prey.
Do you think the same tongue properties are likely to be used across all frog species? Are there any other animals that are thought to use similar/ the same underlying physics?
In our study, we looked at tongue softness across a variety of frog species, and found all to be of similar softness. This leads us to conclude that tongue softness is biologically important for these amphibians. A recent paper on chameleons (Brau 2016) hypothesize that a thin layer of viscous mucus on the chameleon tongue aid in high adhesion during the retraction phase.
How fast does the tongue move, and what is the force of impact?
We found that the frog’s tongue is able to capture an insect in under 0.07 seconds, 5 times faster than a human eye blink. During prey impact, the leopard frog tongue can reach impact speeds up to 4000 mm/s. When the insect is being pulled back into the mouth, the insect acceleration can reach 12 times the acceleration of gravity (in comparison, astronauts usually experience around 3 times the acceleration of gravity during a rocket launch).
Why do you describe the tongue as being like a bungee cord?
As the prey is being reeled back into the mouth, the tongue stretches much like a bungee cord. If you have ever been bungee jumping, you know that as you fall of the bridge, the bungee cord stretches and slows down your fall over time (small amounts of force applied over long periods of time). If you were to tie a rope to your ankle instead, the rope would not stretch, and you would have a large amount of force applied over a short period of time (your ankle would likely come off). As the tongue pulls on the insect, the tongue stretches elastically, storing that energy like a bungee cord, and applying small forces over a longer period of time. This helps to reduce separation forces between insect and saliva.