Grades 3–5 · Organisms
How can a frog’s tongue catch an insect and let it go?
Many frogs capture prey with a tongue coated in special saliva. The tongue can strike an insect and pull it toward the mouth very quickly. Its success depends on both the soft tongue tissue and the coating.
In the diagramA changing coating helps catch and release preyImpact: spreadPull back: holdMouth: releasesoft tongue + saliva whose flow changes with forceEnlarged snapshots of mechanisms studied in some frogs.
During impact, the saliva flows easily and spreads into the insect’s uneven surface. The tongue also changes shape around its prey. Wide contact gives the coating more places to hold than a tiny rigid point would provide.
As the tongue retracts, the saliva resists flow more strongly under the changed forces. The stretchy tongue absorbs and stores some energy, helping prevent the insect from peeling straight off during the rapid movement.
Inside the mouth, forces change again as the frog removes its meal from the tongue. The saliva can flow more easily, allowing release. This changing grip is more useful than a coating that held equally firmly all the time.
About this explanation
Starting knowledge: Know that a moving tongue can touch prey and distinguish a soft surface from a rigid one.
Sources
- Alexis C. Noel and colleagues, Journal of the Royal Society Interface — Frogs use a viscoelastic tongue and non-Newtonian saliva to catch prey