What is the most dangerous animal in the South American rainforest? Is it the top predator, the jaguar? Perhaps the highly venomous Brazilian wandering spider? How about a large caiman, lying in wait just below the surface of the water? Or maybe a huge column of a million army ants? All of the animals above can – and have – killed people in the past, but the animal that has the potential to be the deadliest of them all is a tiny, brightly-coloured frog that hops around in the leaf litter: the poison-dart frog.
Many species of frogs and toads produce poison. Some, if severely irritated, may ooze or even squirt these chemical weapons to deter predator. If a predator is still not daunted and decides to pick the amphibian up in its mouth, the poison may act so swiftly and powerfully on the thin membrane of the mouth that the attacker quickly drops it before it inflicts any serious harm upon the frog. But it is always better, both for the frog and the predator, if engagements of this kind can be avoided altogether; the predator will not waste its time on something that it cannot eat, and the hunted will save its secretions.
The poison-dart frogs of South and Central America, of which there are over 175 species, advertise the fact that they are highly poisonous by sporting extremely vibrant and conspicuous colours, which cover the entire visible spectrum. As a rule, the more brightly coloured a frog is, the more toxic it is. The frogs from the genus Colostethus, also called the rocket frogs, are barely poisonous at all and so they are rather dull in colour to blend in with their surroundings, whereas the highly-toxic golden poison dart frog is a very vivid golden-yellow colour.
In fact, the golden poison-dart frog is not only the most poisonous of the entire family but it is also, quite probably, the most poisonous animal in the entire world (note the difference between a poisonous animal, which uses toxic chemicals as a defence in its body, and a venomous animal, which injects toxins via a weapon – fang, spine, spur etc). The golden poison-dart frog may only be the size of a bottle top, but the skin of just one individual contains enough toxins to kill 10,000 mice, between ten and twenty adult humans, or two African bull elephants. Just holding one in your hand can be lethal, and dogs have even died from touching paper towels that a golden poison-dart frog has previously walked across.
Almost all predators quickly learn the connection between a frog’s colour and its toxicity. For this advertisement to be effective it must be easily seen and so these frogs, unlike most of their cousins, are active throughout the day, moving boldly across the rainforest floor, safe in the knowledge that they are unlikely to be eaten. Indeed, most poison-dart frogs have only one natural predator, the Amazon ground snake, which has developed a resistance to the frogs’ poison and can eat them without ill effects.
But the frogs should also be wary of another inhabitant of the rainforest: Homo sapiens. The local tribesmen capture the amphibians to tip the missiles of their blowpipes with their venom, which is how the poison-dart frogs got their name. To extract the poison from the golden poison-dart frog, the locals make it sweat it out by heating the animal over a flame, protecting their hands with leaves as they do so to prevent any toxins touching their skin. The tips of their dart and arrows are then soaked in the fluid and can keep their deadly effect for over two years. These weapons kill the tribesmen’s prey with extreme speed, and the only reason that the people themselves don’t die from eating game killed by these poison-tipped darts is because the toxins are destroyed by the heat of the fire.
The poison-dart frogs do not actually synthesise these toxins themselves; they sequester the chemicals from the beetles that they eat, which in turn get the poison from rainforest plants. Because of this, it may be that one of the frogs’ prey items, and not the frogs themselves, is truly the most poisonous creature on Earth.