A Painful Mishap Leads to the Discovery of the World’s Only Venomous Frog

September 16, 2015 | Sarah Tse

Photo of a spiny frog skull
Photo credit: The bony spines on this frog’s skull act as extremely effective weapons. Credit: Carlos Jared, Butantan Institute

Two species of frogs are armed with unique weapons that can inject poison directly into the bloodstream, making them the only known venomous frogs.

Although C. greeningi and Aparasphenodon brunoi have been known for decades, scientists had remained blissfully ignorant of their unique weaponry until one scientist got a hands-on lesson earlier this year. Carlos Jared of the Butantan Institute received a painful surprise when he picked up a C. greeningi only to be pricked in the hand.

The helmet of spines sported by the Brazilian frog Corythomantis greeningi looks painful enough on its own, but the spines pack a double whammy by carrying poisonous skin secretions. Luckily, Jared didn’t try to hold onto the frog; if he had, the frog would have used its incredibly flexible neck to squirm around and jab as many spines as possible into his skin.

Although we are aware of many poisonous frogs (like the poison dart frog), C. greeningi, along with Aparasphenodon brunoi, are the first species of frogs known to be venomous. The distinction is simple but important, especially when handling animals. Poisonous animals produce a toxin that may be absorbed through the skin or consumed whereas venomous animals use a more aggressive delivery system like fangs to inject their toxin. For C. greeningi, the frog Jared encountered, it’s the sharp head spines that serve as a method of delivering the poison.

Each spine protrudes from the frog’s skin through a bed of granular skin glands that secretes the toxin. Along with a poison that is powerful enough to kill 24,000 mice with a dose of 1 gram, the secretions contain enzymes that help spread the poison for added potency. Of course, the spines wouldn’t be able to inject a whole gram of poison into a wound, even if the frog could produce that much toxin. But this defense mechanism is still highly effective, especially if a spine should pierce a predator through its mouth.

A. brunoi does not possess as many large spines and glands as does its companion, but it makes up for this deficit with an even more deadly venom that could kill more than 300,000 mice with 1 gram. That makes the venom 25 times more powerful than the kind produced by the much-feared pit viper. Unsurprisingly, scientists are unaware of any predators that would risk snacking on either of these frogs.

These discoveries indicate that many other species of amphibians may exist that can inject their poisons directly into the bloodstream. Several other frogs are known to wield similar spines on their heads, and some salamanders have sharp ribs that can pierce skin. There are so many thrilling possibilities, just waiting to be grabbed by some unsuspecting researcher.

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