The horned frog (Ceratophrys sp.) can consume very large prey items relative to its own body dimensions thanks to the strong pulling action of its sticky tongue. Tongue adhesive forces can be greater than their own body weight and clearly outweigh any potential prey item, a study in this week’s Scientific Reports suggests.
Many frogs have mucus covered sticky tongues that can catch and pull prey into their mouths, although the strength of this action and the mechanism that causes attachment are poorly understood. To measure the adhesive performance of the tongue in frogs of the genus Ceratophrys (Ceratophryidae), Thomas Kleinteich and co-workers coaxed the frogs into firing their tongues by displaying prey behind a pressure sensitive glass panel. They found that the found that the pulling forces are up to three times the body weight of the animals, and show that the strength of the pulling force increases with higher impact pressures and shorter impact durations. Stronger adhesion was associated with lower mucus coverage of the contact area, which suggests that mucus itself may not add simply as some sort of liquid adhesive or glue, and indicates that the surface of the tongue has and important contribution to adhesion.
The authors note that it remains to be seen if frog tongues achieve similar adhesive strengths on surfaces with variable structures and surface chemistries that more closely resemble the properties of natural prey surface materials, such as fur, feathers, or cuticle. However, the experimental data shows that frog tongues can be best compared to pressure sensitive adhesives that are of common technical use as adhesive tapes or labels.