Poisonous many may be, but scientists had yet to discover a species of frog that is venomous. That is, one that not only produces toxic substances, but also possesses a means to deliver them to another organism as a defense mechanism. Finally, a new discovery has put not just one venomous species on scientists’ radars, but two. Both residing in Brazil, these frogs are adorned with bony spines that pierce the skin where their venom concentrates, effectively turning their heads into dangerous weapons.
“Discovering a truly venomous frog is nothing any of us expected,” lead author Edmund Brodie Jr. of Utah State University said in a statement. And that was not the end of the unexpected surprise. Entering scientific literature in true style, the nasty substances they produce were found to be so toxic that they even outrank the venom produced by pit vipers found throughout Central and South America. The fascinating discovery has been published in Current Biology. 
Though many may appear feeble and defenseless, nature often reminds us to not let looks be deceiving: amphibians have toxic tricks up their sleeves. Well, skin. Most amphibian species produce noxious agents contained within skin glands, although some sequester them from their diet. These compounds range in toxicity, from mild irritants to some of the most powerful poisons known.
But while their poisonous nature is no secret, the absence of delivery mechanisms meant that they were not considered venomous, although one salamander is perhaps a tentative exception. It was therefore a rather exciting moment when the researchers discovered that two well-known frog species fell into this category, albeit the tale surrounding this eureka moment is perhaps not one to envy.
Lead author of the study, Instituto Butantan’s Carlos Jared, unfortunately ended up on the receiving end of one the frog’s poisonous secretions while collecting specimens, after the bony skull spines of one broke his skin and resulted in soaring pain for five hours. This particular species is called Corythomantis greening, while the other is Aparasphenodon brunoi. Luckily for Jared, his altercation was with the less toxic species. The secretion from this frog was found to be around twice as lethal as the venom produced by Brazilian pit vipers of the group Bothrops, while A. brunoi’s was an impressive 25-fold more deadly.
Corythomantis greeningi Spines. Jared et al., Current Biology. Photo courtesy of Utah State University.
“We were amazed at the level of toxicity in these frogs,” Brodie told IFLScience. According to their calculations, a gram of A. brunoi’s potent skin secretions would probably be sufficient to end the lives of 300,000 mice, or 80 humans. Needless to say, these frogs have no known predators. But why the need for such a pokey mechanism? Brodie explains to IFLScience that while the substance is extremely toxic, only very small amounts will be transferred by the tiny head spines.
“What we see here is animals using small amounts of very strong venoms to protect themselves from predators,” he added.
Interestingly, Brodie says that other members of the genera to which these two frogs belong do not appear to have these specializations, but the team plans to continue their research by studying other species that they suspect could be venomous.
Although the researchers do not know exactly how the venom acts, this is also something the team is pursuing. Preliminary results indicate that the toxic components are similar to those found in other venomous animals, such as enzymes that are known to be able to trigger tissue damage, Brodie says.
Center image credit: A close-up showing the lip of a Corythomantis greeningi specimen (Greening's frog). Carlos Jared/Butantan Institute
