By Staff Writer: Jerri Clewis
If it bites you and you get sick, it’s venomous. If you bite it and become sick, it’s poisonous. That’s the easy explanation for the difference between venomous and poisonous, but it is not so clearly cut for some species. Amphibians have always been considered more poisonous than venomous, but some recent discoveries are beginning to challenge that.
In 2015, a team of scientists discovered that the Greening’s frog and Bruno’s casque-headed frog, both endemic to Brazil, are venomous amphibians, according to the Natural History Museum. Both species have bony spines in their skulls that pierce the skin when pressure is applied, coating the spikes in their toxic skin secretions that the frogs can then inject into unsuspecting predators. Essentially, these species headbutt predators with venomous attacks, which one of the scientists unluckily discovered when collecting samples.
The victim suffered pain through their arm for five hours, but they had only come into contact with a Greening’s frog—the less toxic of the two.
Bruno’s casque-headed frog has venom that is an estimated 25 times more potent than a Fer-de-lance pit viper. One of the most dangerous snakes in Central and South America, a Fer-de-lance can allegedly inject 105 mg of venom on average in just a single bite, according to Young People’s Trust for the Environment. A fatal dose for a human is only 50 mg, but mortality rates remain low.
The study from the scientists also hinted at the likelihood of other species being venomous despite being classified as poisonous, such as Echinotriton salamanders who have spiny ribs protruding through their skin. Other frogs like the spiny-headed tree frog and Ranwella’s horned tree frog could also be contenders for further study.
Another study in 2020 revealed more potential for the existence of venomous amphibians. Caecilians, similar to earthworms but with rows of teeth, were discovered to have glands in their mouths that secrete saliva suffused with venomous enzymes, according to National Geographic. This could make caecilians the first known amphibians to have a venomous bite, depending on further study of how the glands function in coordination with their fangs.