extremely deadly frog
One gram of this frog's venom could kill 80 people. Carlos Jared/Butantan Institute

Two species of frogs that are more venomous than deadly pit vipers have been discovered in Brazil. Corythomantis greeningi and Aparasphenodon brunoi are the world's first truly venomous frogs and scientists have called their discovery "astounding".

Scientists calculated that a single gram of the toxic secretion from A. brunoi would be enough to kill 80 humans. Both species have been known to science for decades if not centuries, but researchers knew very little about their biology – or their deadly nature. The species are described in the Cell Press journal Current Biology.

deadly frog brazil
C. greeningi's venom is less deadly, but it's spikes are bigger Carlos Jared/Butantan Institute

Study author Edmund Brodie Jr said: "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."

The frogs produce potent toxins that they deliver in harmful secretions through the bony spines on their heads. These spines on their skulls pierce through their skin to deliver the venoms, which are produced by the skin glands. Neither species has any known predators – which is not surprising considering their deadly defence mechanisms.

Brodie and Carlos Jared of Instituto Butantan in São Paulo, lead authors of the study, realised C. greening was venomous when Jared was injured by one of the frog's spines – it caused intense, radiating pain that lasted for five hours. Luckily it was the less-venomous of the two species.

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The spiny heads of the venomous frogs. Brodie/Jared et al/Current Biology

Whereas C. greening's head spines are better developed and its skin glands produce greater volumes of venom, A. brunoi has much more lethal venom.

Speaking o f A. brunoi and its potential to kill, Brodie said: "It is unlikely that a frog of this species produces this much toxin [enough to kill 80 humans], and only very small amounts would be transferred by the spines into a wound. Regardless, we have been unwilling to test this by allowing a frog to jab us with its spines."

The scientist said that although the venom delivery system of these two frogs is less effective than pit vipers, just small amounts could be very dangerous to a would-be predator. They said their results suggest it is likely venomous amphibians "are more toxic and common than previously assumed".

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