We associate poisonous animals with snakes, jellyfish, or certain groups of insects or arachnids. Venom production is a frequent phenomenon in the animal kingdom; fish, octopus, cone snails, centipedes, and even some birds from New Guinea, Australia, and Indonesia and at least one known species of lizard—the Gila monster ( Heoderma suspectum )—can produce venom.
In this long list, amphibians have a special place because they do not use their venom as an attack mechanism, but rather as a defense system, to avoid being eaten. In many cases, such as some species of toads, the toxin is very mild, causing only an unpleasant taste and perhaps a mild reaction in the organism trying to devour it.
But there is a family of frogs from Central and South America that stands out for its vibrant colors and its powerful poison on the surface of its skin: the Dendrobatidae . And among the 203 known species, Phyllobates terribilis, the golden dart frog , lives up to its specific epithet.
The golden dart frog
The golden dart frog is a small amphibian that does not exceed 5 centimeters in length. Despite its small size, it is one of the largest dendrobatids , and one of the easiest to find.
It lives in the tropical forest adjacent to the Pacific coast of Colombia, and currently its population is in serious decline, making it a threatened species; This is how it is classified by the IUCN. Most of the specimens are distributed in a protected area called Rana Terribilis Reserve. Since 1985, Colombian legislation expressly prohibits the extraction of specimens of P. terribilis from the wild.
Despite its obvious danger, the species has a large presence in international trade. However, the majority of individuals are believed to be from captive breeding, and the number of wild-caught commercial golden dart frogs is estimated to be very low. The greatest threats it faces are the loss of habitat due to deforestation —whether due to mining activities, indiscriminate logging or the change of land use for cultivation— and pollution , especially that which comes from agriculture.
The deadliest animal poison
The main toxin produced by the golden dart frog is batrachotoxin, a fat-soluble alkaloid produced by most dendrobatid frogs and some bird species; but P. terribilis does so in the highest concentration of toxin that can be found. A single frog can hold up to 1.9 mg of toxin , enough to kill 45,000 mice. Although there are no studies for human toxicity, it is estimated that this amount would be enough to kill between 10 and 20 people .
It is a neurotoxin , that is, a poison that acts at the nervous level. It is described as an antagonist of sodium ion channels – the proteins that allow the passage of these ions through the cell membrane of neurons. These sodium channels are ultimately responsible for generating the action potential that propagates along the neurons, causing the nerve impulse.
Batrachotoxin induces irreversible depolarization of nerves and muscles, leading to paralysis, fibrillation of the heart muscle, and ultimately heart failure .
The frogs themselves are, however, immune to this toxic effect —although they are not immune to other toxins with a very similar action, such as veratridine, present in plants such as cebadilla—.
Using batrachotoxin
The use of batrachotoxin as a biochemical tool for the study of sodium channels has been proposed . It has also been used as a drug to examine the nervous influence on different tissues. It has been widely used in pharmacological studies, always in animal models, although its use in clinical trials is avoided due to its high toxicity. Its possible use in the future as an analgesic in the form of an ointment, properly prepared, dosed and, perhaps, encapsulated, in such a way that it reaches the target tissue without affecting the rest of the nervous system, is not ruled out . But much previous scientific work will be necessary .
However, there is another use of batrachotoxin that has been developing for centuries. The Emberá indigenous peoples of western Colombia have used the poison of frogs of the genus Phyllobates to poison their blowgun darts , with which they hunt animals. To do this, hunters must be extremely careful not to touch the frog with bare skin, and even less so if they have any injuries —it would be the cause of a fatal accident. They hunt several frogs that they keep in a basket; when they need them, they let one out, and hold it against the ground, with the help of a stick that they hold with their feet. They then stroke the animal’s skin with the tips of the darts to impregnate them with poison, and let them air-dry before putting them away, ready for use.
References:
Carpenter, A. I. et al. 2014. A review of the international trade in amphibians: the types, levels and dynamics of trade in CITES-listed species. Oryx, 48(4), 565-574. DOI: 10.1017/S0030605312001627
Daly, J. W. et al. 1980. Levels of Batrachotoxin and Lack of Sensitivity to Its Action in Poison-Dart Frogs ( Phyllobates ). Science, 208(4450), 1383-1385. DOI: 10.1126/science.6246586
IUCN. 2016. Phyllobates terribilis (e. T55264A85887889) [Data set]. International Union for Conservation of Nature. DOI: 10.2305/IUCN.UK.2017-3.RLTS.T55264A85887889.en
Myers, C. W. et al. 1978. A dangerously toxic new frog (Phyllobates) used by Emberá Indians of western Colombia, with discussion of blowgun fabrication and dart poisoning. Bulletin of the AMNH ; v. 161, article 2.
National Center for Biotechnology Information. 2022. PubChem Compound Summary for CID 6324647, Batrachotoxin.
