The Venomous Nature of Greening’s Frog

This peculiar little amphibian is not just any tree frog; it has an extraordinary way of inflicting pain. When we think of poison dart frogs from the rainforests of South America, we typically envision small, vibrant creatures that warn us of their toxicity. They hang from branches, displaying bright colors reminiscent of hazardous symbols, urging us to keep our distance. If left undisturbed, they won't pose a threat. However, not all frogs provide such clear warnings about their harmful intentions. Allow me to introduce Corythomantis greening, known as Greening’s Frog, a tree frog native to the dry regions of northern Brazil. This frog is eager to cause you harm.

Dr. Carlos Jared, a researcher at the Butantan Institute in São Paulo, had quite the startling encounter while studying local frog species. Unlike many frogs that might flee or release toxins when captured, Greening’s Frog chose to launch an offensive. It repeatedly head-butted Dr. Jared's hand, wriggling to slam its head against his palm. Initially perplexed, Dr. Jared soon realized that the frog’s actions were not just playful; intense pain surged up his arm from his palm to his shoulder. He had to release the frog, but the damage was already done — his arm ached for five hours.

After regrouping and safely securing the frog, researchers took it back to their lab in São Paulo for further examination. Under microscopic scrutiny, the cause of the pain became evident. The frog's head is equipped with bony spines just beneath the skin, poised for action. When it strikes a hard surface — like a researcher’s arm — these spines pierce through venom glands, becoming saturated with venom that is even more potent than that of the Brazilian pit viper. Upon contact, the spines inject this venom through tiny openings in the skin, resulting in rapid and intense pain. For Dr. Jared, this led to hours of suffering, while in the mouth of a predator such as the White-eared Opossum, the venom could be lethal. Remarkably, Greening’s Frog is not the only venomous frog known to science.

So far, two species have been identified as venomous: Corythomantis greening and Aparasphenodon brunoi. The latter, known as Bruno’s casque-headed frog, possesses venom that is 25 times stronger than that of a Brazilian pit viper. As one researcher noted, “We have not yet experienced the effects of the most toxic species and hope we do not.” A mere gram of its venom could be fatal to 80 humans.

The existence of venom in these frogs is not only astonishing due to its potency but also because venom is exceedingly rare among amphibians. While skin toxins, like those found in poison dart frogs, are widely recognized, venom — which must enter the body to inflict harm — is uncommon in this class of animals. Thanks to this evolutionary advantage, these frogs have no known predators and have established a secure niche in the wilderness of Eastern Brazil.