You don’t want to mess with Bruno’s casque-headed frog (Image: Carlos Jared/Butantan Institute)

Meet the two species that just happen to be the world’s first, and so far only venomous frogs.

We knew that some frog species secrete poison onto their skin that can make predators ill if they swallowed them.

But the two species from Brazil have tiny spines on their heads – particularly on their upper lips – that enable them to inject lethal venom directly into the bloodstream of any assailant.


Just a single gram of venom from one of the species – Bruno’s casque-headed frog, aka Aparasphenodon brunoi – would be enough kill 80 people, or 300,000 mice. The frog’s venom is 25 times more poisonous by weight than that of Brazilian pit-vipers.

Venom from Greening’s frog, Corythomantis greening, is less dangerous, but still twice as potent as a pit-viper’s, as Carlos Jared of the Butantan Institute in São Paulo, Brazil, discovered to his cost during a field trip to Caatinga in the state of Rio Grande del Norte.

Greening’s frog: handle with extreme care (Image: Carlos Jared/Butantan Institute)

“Carlos was jabbed by spines while collecting the frog,” says Edmund Brodie of Utah State University in Logan. “Intense, immediate pain radiated up his arm and lasted five hours. He was many hours from any medical services, so just toughed it out.”

The other, more lethal Bruno’s frog was discovered in the dense vegetation of Brazil’s Atlantic Forest in Espirito Santo state but luckily, no one touched it with bare hands this time.

Back in the lab, Brodie, Jared and their colleagues analysed 15 frogs of each species, testing the potency of the venoms by injecting them into mice. They also killed five of each species and took detailed scans of their flesh, skin and skeletons.

This revealed the tiny spines on the faces of both species that take venom from neighbouring glands and inject it into assailants. The spines pierce through the frogs own skin and are abundant on their upper lips.

Unusually, the frogs can wiggle and flex their heads up, down and sideways, and this is how they inject their venom, jabbing their spiny upper lips into their attacker’s flesh.

This takes amphibian defences to a new level, says Brodie. “The intense pain is probably the most important aspect of repelling predators,” he says.

“The finding that some frogs can inject venom more toxic than that of a pit-viper changes how we view these incredible animals,” says Deborah Hutchinson of Seattle University, Washington. “There are likely more species of venomous frogs awaiting discovery.”

This suggest frogs are not as harmless as we think, says Juan Santos of Brigham Young University in Utah. “The presence of these spines suggests that at least some other tree frogs might actively rather than passively defend themselves against attackers,” he says. “This research will open a new line of research into the evolution of anti-predator mechanisms in frogs.”

Brodie and colleagues are now looking for other venomous amphibians to join the club that includes snakes, spiders, scorpions, jellyfish, lizards and komodo dragons.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2015.06.061