What the Frog’s Saliva Does for the Frog’s Tongue

Ig Nobel Prize winner David (“urination duration in mammals”) Hu and colleagues turned their intense gaze toward frog tongues and saliva. They published this study:

Frogs use a viscoelastic tongue and non-Newtonian saliva to catch prey,” Alexis C. Noel, Hao-Yuan Guo, Mark Mandica, David L. Hu, Journal of the Royal Society Interface, 2017, 14, 20160764.

Frogs can capture insects, mice and even birds using only their tongue, with a speed and versatility unmatched in the world of synthetic materials. How can the frog tongue be so sticky? In this combined experimental and theoretical study, we perform a series of high-speed films, material tests on the tongue, and rheological tests of the frog saliva. We show that the tongue’s unique stickiness results from a combination of a soft, viscoelastic tongue coupled with non-Newtonian saliva. The tongue acts like a car’s shock absorber during insect capture, absorbing energy and so preventing separation from the insect. The shear-thinning saliva spreads over the insect during impact, grips it firmly during tongue retraction, and slides off during swallowing. This combination of properties gives the tongue 50 times greater work of adhesion than known synthetic polymer materials such as the sticky-hand toy. These principles may inspire the design of reversible adhesives for high-speed application.

The University of Georgia presents additional details, including this demo and explanation by study lead author Alexis Noel:

BONUS: From an earlier era, focusing higher in the frog’s skull, Jerry Lettvin‘s classic “What the Frog’s Eye Tells the Frog’s Brain

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