A frog whose lack of predators has intrigued scientists for decades has finally given up its secret – by stinging a biologist.
Carlos Jared of the Instituto Butantan and Edmund Brodie of Utah State University were collecting examples of Corythomantis greeningi in eastern Brazil, when one of them stung Jared on the hand, giving him five hours of "intense, radiating pain".
Though nowhere near as deadly as Colombia's golden poison frog, C. greeningi has the advantage of having a delivery method for its venom – bony spines on top of its head.
"Discovering a truly venomous frog is nothing any of us expected, and finding frogs with skin secretions more venomous than those of the deadly pit vipers of the genus Bothrops was astounding," says Brodie.
Perhaps just as surprising is C. greeningi isn't unique – they found another frog in the same area, Aparasphenodon brunoi, that also has venomous spines and – perhaps unsurprisingly – no predators.
Luckily, Jared was stung by the weaker of the two. Calculations suggest a single gram of A. brunoi venom would be enough to kill 80 humans.
"It is unlikely that a frog of this species produces this much toxin, and only very small amounts would be transferred by the spines into a wound," Brodie says. "Regardless, we have been unwilling to test this by allowing a frog to jab us with its spines."
The venom would be even deadlier if applied to the mouth lining, as would occur if something tried to eat it.
Animals which are deadly to eat or touch but can't actively deliver their payload are considered poisonous, not venomous. Luckily, the golden poison frog is merely poisonous – a single gram of its venom could kill 15,000 people.
The researchers suspect many other species of frogs already known to science may also be venomous.
Their findings were published today in journal Current Biology.