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Why Otters Disembowel Toads Before Eating Them

The unfortunate amphibian likely fell victim to an otter, which skinned it to avoid ingesting the deadly toxins found in its glands

Researcher Jack Ashby initially suspected a crow was responsible for the toad's skinning, but after examining the photo, he concluded that an otter was the more likely culprit (Courtesy of Jan Freedman)
smithsonianmag.com

A toad spotted at Venford Reservoir in Devon, England, looks more like a gruesome cousin of Frankenstein’s monster than the croaking amphibian it actually is—or at least once was.

Identifiable as Bufo bufo, or the common toad, by its protruding eyes and stout, wart-covered head, the creature is flipped almost entirely inside out. As seen in a photograph posted on Twitter by museum curator Jan Freedman, its glassy intestines spill out onto the surrounding granite, while its flayed skin, still attached below the jaw, extends over the back of the body.

Freedman, a curator of natural history at the Box museum in Plymouth, England, chanced upon the unfortunate toad’s remains during a family walk through the reservoir, according to Live Science’s Mindy Weisberger. Intrigued by the singular scene, he turned to social media in search of an explanation, writing, “Sorry for the gross picture. This was a toad—but it was turned inside out. I’ve never seen anything like it before—the result of some kind of predator?”

Responses ranged from jokes—one user suggested a “witch did it”—to more serious suggestions. Jack Ashby, a museum manager at the University Museum of Zoology in Cambridge, theorized a crow had flipped the toad over and eaten it “from the belly up” in order to avoid its toxic skin, while Rich Grenyer, a biodiversity scientist at the University of Oxford, pointed out that badgers exhibit similarly brutal behavior toward hedgehogs.

As Steve Wilson reported for Australian Geographic in January 2018, Australian crows are known to avoid the poisonous glands found in toads’ heads and backs by flipping the creatures over, grasping them by the limbs or brow, and pecking away until they reach the toxin-free flesh of the thighs, tongue and intestines. Sometimes, crows must repeatedly roll their victims onto their backs, as the “luckless toad [may try] to hop away.”

Ashby tells Weisberger that he initially attributed the toad’s inverted state to crows because its flesh appeared to be delicately removed, “which one might expect to be more easily done with a nimble beak.” Still, upon closer examination, Ashby decided an animal first suggested by Amy Schwartz, a “road ecology” researcher at Wales’ Cardiff University, was the more likely culprit.

“Otters skin [toads],” Schwartz wrote on Twitter. “You can sometimes see floating skins in ponds when an otter has visited.”

A 2015 study published in Ethology Ecology & Evolution found that skinning toads is an “innate” otter behavior. Although otters are more likely to dine on fish, as Schwartz explains to Weisberger, they are also known to prey on fellow mammals, birds and amphibians. According to the study, toads and frogs are particularly valuable food sources in zones of “low fish production” and during spawning season, when they converge on ponds en masse to breed.

For the research, a team of scientists from Spain’s Universidad de Salamanca and Direcció General del Medi Natural observed two juvenile otters that had never previously encountered amphibians. Over a series of test runs, the otters grew more skilled at attacking and consuming toads without falling prey to the creatures’ toxins. Eventually, the pair realized that the most effective predation strategy was “gaining access to meaty parts and viscera … by means of a ventral incision and skin laceration.”

Speaking with Live Science’s Weisberger, Ashby says that the toad spotted by Freedman and his family likely fell victim to an otter. In addition to missing much of its muscle, leg bone and spine (indicative of being attacked by “something large enough to chew up whole toad legs”), the hapless toad was found alongside an empty sack of skin. Once home to the creature’s leg, the skin was ripped away with enough strength to remove “muscle, bone, tendons and ligaments” in just one piece.

“This requires a serious amount of force, presumably by an animal holding the carcass in its paws and pulling the leg out of its skin by its teeth," Ashby concludes. "It’s a lot easier to imagine an otter doing this [than a crow].”

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