Cane toads swallow their tongue when they eat

The phrase “to swallow one’s tongue” has circulated since at least the 1980s, signifying a variety of things such as falling silent to experiencing a general feeling of fear. While it is anatomically impossible for a human to swallow their tongue, a new study led by the Florida Museum of Natural History has found that cane toads (Rhinella marina) actually achieve this feat every time they eat.

The scientists used X-ray videography to investigate toads’ feeding behavior, offering the first glimpse of what frogs do once their food reaches their mouths. The analysis revealed that cane toads swallow prey by using a complex pulley system of cartilage and muscle that travels so far down their throats, it butts up against their hearts.

“We know a lot about how frogs extend their tongues and how it sticks to their prey, but prior to this study, essentially everything that happens after they close their mouths was a mystery,” said study lead author Rachel Keeffe, who conducted this research as part of her doctoral degree in Biology at the University of Florida.

After placing the toads in a clear observation box, the researchers fed them a steady stream of crickets while filming them using X-ray videography. “We weren’t sure what was happening at first,” Keefe explained. “The whole floor of the mouth was pulled backward into the throat and the tongue along with it.”

Examining meticulous reconstructions of movements into 3D animations, the scientists observed that once the toad’s tongue has reached its fullest extent, the hyoid – a cartilaginous plate with loops and prongs attached to muscles on the floor of their mouths – retracted into their throats. Then, the tongue, which is directly attached to the hyoid, was slingshot back into the mouth. It still remains unclear how far back the hyoid can move, since its path is blocked by the toad’s heart, which the animal slides up against milliseconds before the tongue and its attached prey smash into the cartilaginous cushion.

Finally, in order to dislodge the concussed insect from its sticky tongue, the toad uses what the experts call a “hyoid dorsal ascent.” “The hyoid shoots up and presses the tongue against the roof of the mouth, after which it moves forward, essentially scraping the food off into the esophagus,” Keefe explained. The entire feeding process takes less than two seconds, with most of the time spent repositioning the tongue and hyoid after swallowing.

Since there is a rich diversity of feeding mechanisms among the over 7,000 known frog species, further comparative studies are needed to clarify whether the feeding behavior of cane toads is the rule or the exception.

The study is published in the journal Integrative Organismal Biology. 

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By Andrei Ionescu, Earth.com Staff Writer

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