Venomous frogs use their bony faces to poison predators

Venomous frog (Aparasphenodon brunoi).
© Carlos Jared/Butantan Institute. Venomous frog (Aparasphenodon brunoi).

It’s a widely known fact that some species of frogs are poisonous, but scientists recently discovered that two species of Brazilian frogs are also venomous.

What’s the difference between a poisonous frog and a venomous frog? For an animal to be venomous, it must have some sort of delivery system, like a viper’s fangs. Two species of frogs, Aparasphenodon brunoi and Corythomantis greeningi, use bones that pierce the skin of their faces to stick predators with poison. Non-venomous frogs have poisonous skin, a kind of passive protection against predators. Both A. bruno and C. greeningi are still also considered poisonous, thanks to toxic secretions on their skin—but they also have a way to deliver that poison.

C. greeningi© Carlos Jared/Butantan Institute. Skull of C. greeningi.

Carlos Jared, a herpetologist at the Instituto Butantan in Brazil, discovered this frog's venom first-hand. While collecting C. greeningi, one of the captive frogs jabbed him with its head, rubbing in a sticky secretion of toxins. The resulting injury caused “intense pain radiating up the arm, lasting about 5 hours,” writes Jared in a paper about the discovery.

He also observed that the frogs have an unusual ability to flex their heads up and down and side to side, allowing them to use their bony weapons better. This action would be even more effective inside a predator’s mouth, the researchers note.

Fortunately, Jared experienced the sting of the less poisonous of the two species. The researchers performed experiments to learn more about the frogs' venom, including injecting lab mice with the toxin to find out its potency. The poison of the C. greeningi--the one the researcher experienced--is about twice as deadly as a venomous Brazilian pit viper. However the secretion of the A. brunoi is much stronger, about 25-times more lethal than the pit viper.

Corythomantis greeningi© Carlos Jared/Butantan Institute. A head close-up a Corythomantis greeningi

There is still a lot that we don’t know about these species of frogs. For example, it’s unclear what animals prey on them, and why their toxic secretions are so potent. Edmund Brodie, a biology professor at Utah State and one of the paper’s co-authors, tells GrrlScientist that there might be a predator with some resistance to the the toxin. “Another possibility is that very small amounts [of toxin] would be transmitted by the head spines.”

The paper discussed in this article, “Venomous Frogs Use Heads as Weapons” by Jared et al., is published in Current Biology and can be found here.

Tags: Animals | Nature Blows My Mind

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