Also known as "Poison Arrow Frogs", "Dart Poison Frogs", "Poison Frogs", "Dendrobatid Frogs", (or just dart frog
), Poison Dart Frogs are defined as frogs of the family Dendrobatidae that inhabit the rain forest
s of Central America
and South America
. The family Dendrobatidae is divided into Aromobates, Colostethus, Dendrobates, Epipedobates, Minyobates and Phyllobates. There are more than eighty different species
of these brightly colored frogs
, including the Golden Poison Dart Frog
They are quite small, rarely larger than two inches. They exhibit what is called aposematic coloration; their contrasting hues, including orange, purple, red, yellow, blue and/or green, serve as a warning to predators. Although their bright patterned colors may make you want to hold them, they can be lethal.
Almost all of them produce poisonous secretions from glands in their skin, some of which can be highly potent neurotoxins. The poisons secreted range from merely tasting very bad to causing paralysis or death. These stronger poisons are used by indigenous tribes as a dart or arrow poison, hence the name.
In contrast to most other frogs, these frogs are diurnal. Their diet consists of ants, termites and other small insects and spiders. While most frogs lay hundreds or thousands of eggs, poison dart frogs lay only a few at a time.
These frogs have also been part of the debate over possible advances in medicine that might be found in the rainforest. Besides its use in weapons in the Amazon basin for hundreds of years, frog poison is also known to occasionally be applied to self-inflicted burns to produced a hallucinogenic effect. Native hunters say that the venom can produce a heightened sense of awareness. Certain alkaloids, the bitter, toxic, non-protein compounds most frequently found in plants, but also present in the frog toxins, have been proven to be effective as anesthetics. Morphine is a key example of such a chemical.
Only three species contain levels of toxin that pose a threat to humans. These are Phyllobates aurotaenia, Phyllobates bicolor and Phyllobates terribilis. Phyllobates terribilis is an extremely toxic frog from the Choco region of Colombia. It is uniformly metallic golden yellow in color and produces an alkaloid toxin called batrachotoxin that is extremely toxic to humans as well as other animals. An adult in the wild has enough toxins in its skin to kill 2000 mice. It is estimated that as little as 0.2 µg of batrachotoxin in the human blood stream causes death. This species, along with P. aurotaenia and P. bicolor are used by the Embre Indians to poison their blowgun darts for hunting. The toxin on these darts can remain lethal for up to two years.
Of the toxins found in Dendrobatid Frogs, batrachotoxin, histrionicotoxin, pumiliotoxin, and epibatidine are among the most significant. These alkaloids are known in nature only in amphibian skin, except for homobatrachotoxin, which was recently identified in the feathers and skin of a bird. Batrachotoxin is the most deadly of these and the dominant toxin of the Phyllobates genus.
Batrachotoxin, a complex steroidal alkaloid, is one of the most toxic small molecules known. Levels of the batrachotoxin alkaloids differ greatly among Phyllobates, they range from barely detectable in P. lugubris to P. terribilis which can contain up to 1.9 mg per specimen. It irreversibly blocks the inactivation of sodium ion channels in the cell membrane of nerve and muscle cells. This depolarizes the nerve cells, so they cannot transmit messages, and freezes muscles cells in an activated, contracted state. This produces, among other things, heart arhythmia and respiratory failure. Death is usually the result of heart failure. The lethal subcutaneous dose of batrachotoxin for a mouse is only 100 nanograms. As P. terribilis contains 20 times the concentration of this toxin than any other species displays, it is considered to be one of the most toxic animals in the world.
Levels of batrachotoxin tend to be reduced when P. terribilis is maintained in captivity, but even after being confined for up to 6 years, these frogs were still at least five times more toxic than other Phyllobates species used for their poison. Batrachotoxin was not detectable, however, in P. terribilis frogs bred to maturity in captivity.
The frogs themselves, are not affected by the toxin, though. The nerves and muscles of both wild-caught frogs and those bred in captivity were insensitive to batrachotoxin, though they were responsive to other toxins (not contained in frog skin), that affect the regulatory site controlling sodium channel activation. This implies that immunity to batrachotoxin in these frogs is genetic and not built up desensitization.
One particular compound in the cocktail of toxins found in these frogs has shown some promise in the lab for possible beneficial uses. In tests on mice epibatidine proved to be 200 times as effective as morphine in blocking pain. The chemical also worked in a totally different way from morphine and other opiates, which could be seen because its power was not diminshed when it was administered along an opiate blocker. These findings started off a race to synthesize epibatidine, as a first step toward producing a long-sought after drug: a powerful non-sedating, nonopiod painkiller. Three groups of researchers were successful, one group even produced a version chemically identical to naturally occuring epibatidine. This achievement means that researchers will now be able to work with large quantities of the compound to try to figure out how it works, and won't have to rely the miniscule amount from somewhat rare frogs. Although tests show that epibatidine is itself too toxic to be a human painkiller, by slightly modifying molecular structure, it might be possible that scientists could create a painkiller that acts like epibatidine, without being toxic.
Time is running out for research, however. As the destruction of the frog's habitat continues, these frogs, while not endangered species, are becoming harder and harder to obtain from the wild, where they are at full potency. Meanwhile, most of their toxins have yet to be exactly reproduced in the laboratory. Cases of synthesis, such as that of epibatidine are wonderful, because it means that we can research the benefits for humans, without hurting the frog population.
Anyway just remember folks: They are pretty, but don't touch.