A South American toad species gobbles up venomous scorpions – and it is unfazed by a dose of venom equivalent to 10 scorpion stings.
Carlos Jared and his colleagues at the Butantan Institute in São Paulo, Brazil, studied yellow cururu toads (Rhinella icterica) – named after the male’s colouration and melodious call – as they feasted on yellow scorpions (Tityus serrulatus).
Both animals are common in Brazil, but until now only anecdotal observations suggested these toads prey on scorpions. This is the first study of the behaviour.
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“I was surprised at the toads’ great ability to eat scorpions as if they were any other inoffensive prey,” says Jared. “In humans, a single sting from the yellow scorpion causes terrible pain and can even kill, especially children and the elderly.”
Brazil now has around 156,000 scorpion sting cases annually, the main offender being the yellow scorpion. Shrinking habitats have forced them into cities where they lack predators. Females can reproduce asexually without a male, helping them proliferate.
Meanwhile, the toads are often persecuted with salt and bleach for being “repugnant pests”. Jared hopes they will now receive praise as natural scorpion-exterminators.
After placing them in large plastic boxes with a layer of soil at the bottom, the researchers gave 10 toads two chances to catch and eat a yellow scorpion within a 5-minute period. Seven toads ate both scorpions, two ate just one and one toad didn’t catch any.
Videos showed that, before swallowing, a toad would swiftly load a scorpion into its mouth with its tongue, front legs and jaws. Analysis of the footage suggests that the toads were stung inside the mouth, yet they remained unharmed.
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To see if the scorpion’s venom affects the toads, the researchers injected them with five times the dose that would kill a mouse – or the equivalent of 10 scorpion stings. All survived and seemed unshaken.
“What I find most surprising is that even high doses of venom did not change the toads’ behaviour,” says Arie van der Meijden at the University of Porto in Portugal. “They must have a very efficient resistance to the neurotoxic components in the venom.”
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