Horned frog's tongue has super-frog powers for capturing heavy prey
If your tongue was as sticky as one South American frog's tongue, you could grab a 400-pound object and pull it inside your mouth, say German researchers who've researched the amphibians' mouths.
South American horned frogs have a muscular tongue that sticks to prey like adhesive tape, but with force so strong it can capture and haul in something weighing three times what the frog weighs, researchers at Christian-Albrechts-Universitat-Kiel in Kiel, Germany, found.
That allows the frogs to capture and consume not only insects but prey as large as rodents, snakes, other frogs, lizards and even small birds.
For the study the researchers set up an experiment intended to measure the amount of force the horned frogs, scientific name Ceratophrys sp., could wield in their tongues.
In the experiment, four frogs were offered a cricket at mealtimes, but there was a catch; the insect was behind a glass microscope slide containing sensors to gauge the impact force and contact area of the frog's tongue.
Most frogs have tongues with around a fifteenth the adhesion power of the feet on a gecko -- a famously sticky creature, researcher Thomas Kleinteich says.
"However, in terms of prey capture, [horned] frog tongue adhesive forces are enormous -- on average, 1.4 times their body weight," he says.
"Translated into human dimensions," he said, "that would be an 80-kilogram [176-pound] person lifting 112 kilograms [246 pounds] just by using his or her tongue," he says. "And they do this within milliseconds" of the tongue making contact.
The sticking technique in a frog tongue is similar to that of pressure-sensitive adhesives such as those used on sticky labels and tapes, the researchers said.
The sticking power of the tongue is determined by how hard it hits its intended prey target and how large the contact area is, they said.
Rather than go out and hunt for prey, horned frogs prefer to lie in wait in a burrow, keeping still and waiting for prospective prey to come close enough to be in range of the amphibian's sticky mouth weapon.
With their massive mouths that can gobble up large prey, horned frogs have garnered the nickname "Pac-Man" frogs.
It makes sense the frogs have evolved tongue adhesion force that exceeds the weight of their prey, Kleinteich says, because any prey stuck to the tongue will naturally attempt to pull away and escape.
He says he plans to continue his research, focusing on different frog species and analyzing their anatomy to determine hunting and feeding patterns.
The article was published in the online, peer-reviewed journal Scientific Reports that is a primary research publication from the publishers of Nature.