How frog tongues work

By AG STAFF | March 28, 2018

Frogs use a unique kind of reversible saliva combined with a super-soft tongue to hold onto prey, new research has found.

FROGS ARE RENOWNED for catching prey at high speeds – faster than a human can blink, hitting their unsuspecting meals with a force several times greater than gravity. 

But while previous studies have suggested the frog tongue holds on to its prey by working like sticky tape, such adhesives struggle to work on textured surfaces like that of insects. Instead, new research published this week in the Journal of the Royal Society Interface has found frogs use a unique kind of ‘reversible’ saliva combined with an ultra-soft tongue to hold onto prey.

The researchers, from the Georgia Institute of Technology (Georgia Tech) in the USA, filmed frogs eating crickets in super-slow motion to better understand the physics of the tongue. They also collected saliva samples and measured the softness of the tongue tissue.

frog prey

A northern leopard frog catches a cricket (Image: Candler Hobbs)

They found that frogs’ saliva turns from watery to thick and sticky during prey capture, then thin and watery again as the prey is released inside the frog’s mouth – allowing it to flow on impact, and grip during retraction. The researchers also determined that the tissue of a frog’s tongue is incredibly soft – as soft as brain tissue; 10 times softer than a human’s tongue, enabling it to stretch and store energy like a spring.

“The tongue acts like a bungee cord once it latches onto its prey,” explained Alexis Noel, a Georgia Tech mechanical engineering PhD student who led the study.

“When the tongue first hits the insect, the saliva is almost like water and fills all the bug’s crevices. Then, when the tongue snaps back, the saliva changes and becomes more viscous – thicker than honey, actually – gripping the insect for the ride back. The saliva turns watery again when the insect is sheared off inside the mouth,” said Alexis.

The combination of saliva and tissue softness is so effective, it provides the tongue with 50 times greater work of adhesion than synthetic polymer materials. The findings could help engineers design new reversible adhesives at high speeds, using the same principles.

“Most adhesives that have been created are stiff, especially tape,” said David Hu, a professor at Georgia  Tech and Alexis’s supervisor. “Frog tongues can attach and reattach with soft, special properties that are stickier than typical materials. Perhaps this technology could be used for new band-aids. Or it could be used to create new materials in soft manufacturing.”

Find out more about these findings in this video from Georgia Tech:

Source: Georgia Tech / YouTube

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