First Venomous Frogs Found, With Poison Spines on Head

Greening’s frog has sharp spines that can deliver venom, making it the first known “venomous” frog. Carlos Jared/Butantan Institute

If you're hanging out in Brazil's caatinga, a shrubland in the country's northeast, you may not want to mess with the frogs you find there. Two species of hylid frogs living in the region possess spines on their head that allow them to inject potent poison into the bodies of attackers, according to a study published Thursday in the journal Current Biology.

Although there are many known types of poisonous frogs, which produce toxins capable of killing predators that try to eat them, this is the first known "venomous" amphibian, with the means to delivering the juice pre-emptively, says Edmund Brodie, a study co-author and biologist at Utah State University.

The frogs do this with sharp, bony ridges along the edge of their faces, adjacent to venom glands. Brodie found this out the hard way while working with the (luckily) less-venomous species of the two, Greening's frog (Corythomantis greeningi), which jabbed him in the hand, causing "intense pain lasting five hours," he says.

The venom produced by the second species, Bruno's Casque-headed frog (Aparasphenodon brunoi), is much more dangerous; it's 25 times more lethal than that of Brazilian pit vipers. The former is green and spotted, while the latter has stripes of ocher and dark brown. Both have large eyes and are about 3.5 inches long.

The skull of a Greening’s frog, showing the sharp spines. Carlos Jared/Butantan Institute

A single gram of A. brunoi's venom would be enough to kill 80 humans, although Brodie says it's unlikely a single frog could make this much, and, anyway, a single jab would introduce only a very small amount. But nobody has volunteered to let himself be head-butted by these venomous little buggers.

Both of the frogs have an unusual ability to flex their head toward an attacker, according to the study. The researchers presume that head-butts from these frogs would be especially damaging when applied to the mouth or gums of an assailant.

The study's finding is "mind-blowing," especially since the frogs have been known—but not fully described—for some time, says Joseph Mendelson, director of research at Zoo Atlanta and an amphibian biologist at Georgia Tech, who wasn't involved in the study. "There are thousands of poisonous species of frog, but this one completely changed the rules of the game. When I teach I always make the point that there is nothing that some amphibian doesn't do, and this is just unbelievable, incredible."