According to new research, the pulling force of a frog’s tongue can be up to three times the animal’s own weight. Zoologists placed the horned frog, a predator known to swallow whole mice, in front of a glass slide and tempted it with a tasty cricket. Stronger pulling forces were measured when contact with the glass was briefer and less mucus was left behind. The study suggests that the action of the tongue is similiar to sticky tape.
“It’s the first time we’ve ever measured how well frog tongues stick,” said Dr Thomas Kleinteich, who performed the experiments at the University of Kiel in Germany.
Dr Kleinteich works in a group that studies biological adhesives, including gecko and beetle feet, with a view to finding new designs for sticky applications like boot soles, tapes and parcel closures.
“The thing that’s interesting about frog tongues is that they’re really fast,” he told BBC News. “It only takes milliseconds.” The South American horned frog in particular, a popular pet, is known for its ability to snatch morsels up to half its own size – from locusts and fish to other amphibians and small rodents. In the wild, they lurk half-buried in wait for their prey, and then “they swallow pretty much everything that fits into their mouths,” Dr Kleinteich said.
On average, these forces were larger than the weight of the frog itself, and in the case of one young amphibian more than three times larger. After each trial, the equipment was removed and the frog got its treat. Dr Kleinteich ultimately needed twenty measurements from each frog, so the predators had to be kept happy. Looking at the slides afterwards, the “tongue print” left behind on the glass slide offered more insights, including massive variation in the proportion of the contact area that was covered by mucus. The tongue prints left behind showed varying degrees of mucus coverage
“The common belief is… that the mucus acts as some sort of superglue,” Dr Kleinteich explained. “But what we found was actually that we got higher adhesive forces in trials where we found less mucus. That was quite interesting.”
The mucus appeared to build up over time, so that cases where the tongue touched the glass for longer left more mess behind. “But during the initial contact, the mucus coverage was rather low,” said Dr Kleinteich. “So to actually establish the contact, there might be very little mucus involved.”
“It plays a role. It’s definitely a wet adhesive system, it’s not just structure and friction, because there is some fluid involved. But the key is the structure plus the mucus.
“It’s not like having a liquid glue, it’s rather like a sticky tape.”