Steve's Herpetological Blog

An insight into the life of Steve, his research and the many books he reads

#SciFri

#SciFri: Revenge of the venomous frogs

Something I’ve noticed making the rounds on social media again is the story of venomous frogs, first discovered back in 2015. Yeah you read that right, at a time before the world had started to fall apart/was on fire all the time. This was a pretty big deal at the time and I’m surprised that it hasn’t translated into more awareness 5 years later. Some of you may remember that I first started blogging in 2015 for The Wandering Herpetologist, a now defunct herpetological blog. One of the first big stories I covered back then was the news of venomous frogs being discovered. The fact I’m revisiting it gives this post it’s title so I hope you enjoy.

Before we go any further, we need to deal with a pet peeve of mine. That is the differentiation of poisonous and venomous as some people (including the media) seem to think they are interchangeable. In the most basic definition, something that is poisonous is something that produces a toxin that when you eat it, makes you ill or you know, kills you. Think of arsenic or toadstools here, you eat them you die. That’s a poison. A venom on the other hand is a still a toxin but it has a delivery mechanism to deliver it into the bloodstream of the target such as the fangs of a snake or the telson of a scorpion. There are few factors that make things slightly complicated as some poisons can be absorbed through the skin, for now just pretend you didn’t read that.

Now back to the froggos, which is what we’re all here for and not a rant about the improper use of the word poisonous. Up until 2015, only poisonous amphibians were known. The most colourful and well known of these are the poison dart frogs (it’s literally in their name) although a whole host of bufonids, salamanders and other amphibians also produce toxins in their skin that make them poisonous. Of the 7200 anurans known to science (as of today), only two are venomous (or at least we’ve been able to demonstrate) that they are. So think how crazy it is that those two species both inhabit similar environments in Brazil. Something tells me that the same selection pressures have acted on both species in just the right quantities to produce this truly bizarre adaptation not once, but twice.

How do the species deliver their venom I hear you cry. The frogs have tiny spines on their heads that also protrude from the upper lips. These enable the frogs to essentially headbutt a potential threat or assailant and inject them with their venom. Now there are a number of deadly venomous animals, so much so that we rarely think of non-lethal venomous animals (or plants). How deadly are these little venomous frogs? A single gram of venom from Bruno’s casque-headed frog, (Aparasphenodon brunoi) would be enough kill 80 people. Even for the Neotropics, that is a crazy level of lethality. The frog’s venom is 25 times more toxic by weight than that of the Brazilian pit-viper (Bothrops jararaca).

Venom from Greening’s frog (Corythomantis greeningi), the second of the two species, is thankfully less dangerous although it is still twice as potent as the pit-viper’s. It’s not currently known if the frogs produce their own venoms or sequester them from their diet (as other amphibians do with their poisons). So how did we find out that two species that have been known to science for over 100 years were venomous? A researcher called Carlos Jared from the Butantan Institute in São Paulo, Brazil, was out doing what many herpetologists do – collect specimens. When a Greening’s frog headbutted him and pain started to radiate up his arm. Little did he know he’s just discovered the first venomous frog known to science.

Despite the fact all of this dropped in 2015 (like Immortalised by Disturbed or Drones by Muse), there are still a number of unanswered questions. We don’t know if there are other species of venomous frogs or why these two we do know about evolved in the first place. It’s also not known what animals in the environment these venom systems have evolved for and if any are immune. So future herpetologists, it seems we’ve found you a research project to get stuck into! If you’re looking for something to read this weekend, you can find the original paper here.

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Banner Image: Carlos Jared/Butantan Institute

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