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Venomous Frogs

Venomous Frogs Photo Credit: Carlos Jared/Butantan Institute

A tropical frog delivers a painful surprise.


Transcript

Frogs that could make you croak. I’m Bob Hirshon and this is Science Update.

A Brazilian herpetologist recently discovered the first venomous frog. And according to his colleague, Utah State University herpetologist Edmund Brodie, he did it the hard way.

Brodie
Carlos Jared grabbed one of these frogs, and it jabbed him, and it caused excruciating, immediate pain that radiated up his arm.

In the journal Current Biology, the researchers explain that when threatened, the frog presses spines in the front of its skull right through poison glands in its upper lip, and into the skin of its attacker. Brodie says the toxin is twice as powerful as that of the deadly Brazilian pit viper. And while Jared survived his encounter, he’s fortunate he didn’t grab a second species of venomous frog the team found: it has venom twenty-five times more potent than the first. I’m Bob Hirshon, for AAAS, the science society.


Making Sense of the Research

You've probably heard of poisonous frogs before. But, have you ever heard of venomous frogs? There are approximately 220 species of poisonous frogs in the world. Until recently, though, scientists did not realize that there were venomous ones as well. Indeed, the two venomous frogs that have been discovered so far were found by accident. The herpetologists studying them did not realize that they were venomous and were trying to capture them using their bare hands. When one of the frogs pierced Dr. Carlos Jared's hand, it took him by surprise—and caused him a lot of pain.

In general, frogs don't have many ways to defend themselves against predators. For most species, they either use camouflage, try to intimidate predators, or try to evade predators. Some species of frogs, however, have evolved poison glands in their skin. In most cases, these toxins aren't strong enough to discourage predators. But certain frogs in Central and South America, like poison dart frogs, have especially strong poisons in their skin. The most poisonous is the golden poison frog, each of which contains enough poison to kill eight people.

In contrast to poisonous frogs, venomous frogs actually have delivery mechanisms that can introduce the toxins into other animals. The two frog species that have been studied so far, Greening's frog (Corythomantis greeningi) and Bruno's casque-headed frog (Aparasphenodon brunoi), were discovered in Brazil. Greening's frog was found in Caatinga in the state of Rio Grande del Norte while Bruno's frog was found in Brazil’s Atlantic Forest in Espírito Santo state. The herpetologists analyzed 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.

During their examination of the frogs, they found tiny spines on the faces of both species that take venom from neighboring glands and inject it into predators. The spines pierce through the frogs' own skin and are abundant on their upper lips. They inject their venom by jabbing their spiney upper lips into their attacker's flesh. They also found that the Bruno's casque-headed frog’s venom is 25 times more poisonous by weight than that of Brazilian pit vipers.

This important discovery suggests that frogs aren't as harmless as scientists believed and will likely open up new lines of research into how the ability to defend themselves evolved in frogs.

Now try and answer these questions:

  1. What is the difference between a poisonous frog and a venomous one?
  2. What kinds of mechanisms do frogs use to try to defend themselves?
  3. What did the herpetologists discover about the two species of venomous frogs that they studied?
  4. Do you think there are other venomous frogs out there? How would you go about studying them?

In Amphibian Avenger: Smithsonian Scientist Brian Gwatwicke, you can learn about the problem of the vanishing Panamanian golden frog.

You can read the Weird and Wonderful Creatures: The Titicaca Water Frog to learn about the world's largest aquatic frog.

In the Spotlight on Science Writers: Sandra Markle blog post, Markle shares how she became interested in golden frogs dying at alarming rates and their unknown killer.


Going Further


For Educators

You can extend the learning from this Science Update by leading your students through these Science NetLinks lessons:


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