Poison Dart Frogs: How Poisonous Are They?
| Wildlife & Flora
Poison dart frogs have long been used by the indigenous peoples of South America. They learned centuries ago that rolling a blow-dart or arrow tip over a live frog’s skin creates a coating of poison that can paralyze any animal, making it easier to hunt. Such weapons have also been known to be used to combat enemy tribes and the conquistadors.
Why are they poisonous?
The frogs on the other hand don’t use this poison to hunt at all, but have developed it as a self-defense mechanism to ward off predators. The frogs not only taste vile but will also kill any predator that eats them*.
The poison is an alkaloid toxin called batrachotoxin that the frogs accumulate based on their diet of termites, ants, and other invertebrates. Scientists think a small beetle from the Melyridae family that produces the same toxin may be the crucial diet ingredient. The toxic chemicals generated from eating these microfauna are secreted by the frogs through their skin.
* There is one snake species (Liophis epinephelus) which is resistant, but not completely immune to the frog's poison.
Why don’t the frogs get poisoned?
The frogs are immune to their own poison. Batrachotoxin attacks the sodium channels of cells, but these frogs have special sodium channels the poison cannot harm. The poison is stored in its skin glands and can be stored for years, as such toxins do not readily deteriorate. That’s why the tips of arrows and darts soaked in these toxins can keep their deadly effect for over two years.
How poisonous are they?
Many frogs contain mild toxins that make them unpalatable to potential predators. The chemical make-up of toxins in frogs can vary from irritants to hallucinogens, convulsants, nerve poisons, and vasoconstrictors. Poison dart frogs are especially toxic. Their toxins can prevent an animal’s nerves from transmitting impulses, leaving their muscles in an inactive state of contraction. This can lead to fibrillation and heart failure.
However, the levels of toxicity vary considerably from one species to the next. Of over 175 species, only three have ever been documented as being used by the indigenous tribes for the purpose of hunting (curare plants are more commonly used). These three come from the Phyllobates genus, which is characterized by the relatively large size and high toxicity levels of its members.
The most toxic of poison dart frog species is the Phyllobates terribilisor commonly called Golden Poison Frog, although it can come in green, white, yellow or orange colors. It is probably the most poisonous animal on Earth. Even though it is a mere 5cm long, it has enough poison to kill 10-20 adult humans, 20,000 mice or 2 African bull elephants. Only 2 micrograms of this lethal toxin (the amount that fits on the head of a pin) is capable of killing a human or even a jaguar.
The Black-Legged Dart Frog (Phyllobates bicolor), also known as the Bicolored Dart Frog, is the second most toxic of the wild poison dart frogs. This species is 3 - 4cm in length and obtained its name on account of its normally yellow or orange body, with black or dark blue hindlegs and forelimbs below the elbow. Some bear a striking resemblance to the Golden Poison Frog.
The Kokoé Dart Frog (Phyllobates aurotaenia) has roughly the same level of toxicity as the Black-Legged Dart Frog. This species is 3 – 3.5cm in length and has a black ground color, with two thin golden, orange, or green dorsolateral stripes extending from the base of the thigh and meeting at the snout. This species does not occur in any protected areas and is rapidly losing its habitat.
Interestingly, if you were to breed these frogs in captivity, they would not be poisonous as their diet would be so different to that in the wild that the toxins would not be formed.
Why the bright colors?
Known as the jewels of the rainforest, what these tiny frogs lack in stature (most are about the size of a quarter), they more than make up for in color. They areaposematic (from apo- away, andsemantic sign) meaning they have developed their bright coloration as a warning of their unpalatability to ward off potential predators.
Being a diurnal species (they sleep at night), they show off these vibrant colors in the light of the day for maximum effect. There is a strong correlation between the levels of coloration and amount of alkaloid toxins the frogs have, although the jury is still out on this as there are at least two non-poisonous frog species that use similar coloration to poison dart frogs for self-protection.
Recently, toxins isolated from poison dart frog skin samples have been found to have valuable medicinal uses. Some medicines produced on the basis of batrachotoxin are already being used as anesthetics in surgery. Toxins produced by the Phantasmal Poison Dart Frog (Epipedobates tricolor), a species native to Ecuador, enabled researchers to develop a synthetic compound that shows promise as a painkiller more effective than morphine, but non-addictive.
In another example, the skin of the Strawberry Poison Dart Frog (Oophaga pumilio) contains compounds that have been reproduced in the laboratory for use as a cardiac stimulant.
Many species of poison dart frog are endangered due to loss of natural habitat. Let's hope that these medical properties will mean the human race will value these tiny, yet incredibly beautiful amphibians much more, so future generations will witness them in all their splendor.