The tongue of some horned frogs are so sticky, they can pull in prey weighing three times as much as the animal doing the hunting.
Frogs in the genus Ceratophrys are sit-and-wait predators, who only strike when prey comes to them. They eat a wide variety of other animals, including snakes, lizards, rodents, and even other frogs. Striking with their tongues, they need to pull in creatures covered in scales, smooth skin or fur. Only that way, can the prey be drawn into the mouth of the frog.
Researchers from the Christian-Albrechts-Universität-Kiel studied adhesion of frog tongues to glass.
Thomas Kleinteich and Stanislav Gorb placed four horned frogs in a glass pen. They then put a cricket behind a glass sensor, set to measure the forces of impact. Frog tongues struck the glass with a impact up to three times the weight of the animal. Immediately, the tongue started withdrawing, pulling back with as much as 1.45 times the frog's own weight.
Researchers then studied the tongue print left by the animals on the glass. This allowed them to calculate the amount of surface area of the tongue that came in contact with the plate, as well as other data.
"Surprisingly, we found that the tongues adhered stronger in feeding trials in which the coverage of the tongue contact area with mucus was relatively low," investigators wrote in an article announcing their findings.
Some species of frogs, along with humans, have tiny bumps and hairs on their tongues called Papillae. Kleinteich told the press he is uncertain if similar structures in frogs could aid in increasing adhesion.
This finding led researchers to the idea that other aspects of the tongue, including surface area, could play a wider role in adhesion than once believed. The team compared the adhesive properties of frog tongues to pressure-sensitive adhesives (PSA's), such as household tape.
Horned frogs are also known as Pac-Man frogs for their large mouths. Smaller prey is captured with the tongue and pulled directly into a frog's mouth. Larger animals are immobilized by the tongue before being consumed. Although it may be possible for these animals to capture prey larger than itself, they are still unable to eat anything much more than half its size.
The Z-Man program, developed by the Defense Advanced Research Projects Agency (DARPA), recently announced the creation of paddles that allow users to climb vertical walls like a gecko.
Study of adhesion in horned frogs was detailed in Scientific Reports, hosted by the journal Nature.
