– if any – predators. The snake species Leimadophis epinephelus has shown resistance to several frog toxins including batrachotoxin, and has been observed to eat juvenile frogs without ill effects. Toxicity The golden poison frog is the most poisonous animal on the planet; these frogs produce deadly alkaloid batrachotoxins in their skin glands as a defense against predators. To become poisoned a predator generally must attempt to consume the frog, although this species is so toxic that even touching an individual frog can be dangerous. This extraordinarily lethal poison is very rare. Batrachotoxin is found only in three poisonous frogs from Colombia (all genus Phyllobates), a few birds from Papua New Guinea, and four Papuan beetles of the genus Choresine in the family Melyridae. Batrachotoxin affects the sodium channels of nerve cells. While it is unknown how the frog avoids poisoning itself, other species of poisonous frogs have been demonstrated to express a "toxin sponge" protein in blood plasma, internal organs, and muscle that binds and sequesters the toxin so as to prevent autointoxication. Mechanism Batrachotoxin binds to, and irreversibly opens, the sodium channels of nerve cells leaving the muscles in an inactive state of contraction, which can lead to paralysis, heart fibrillation, heart failure, and death. The average dose carried will vary between locations, and consequent local diet, but the average wild golden poison frog is generally estimated to contain about one milligram of poison, enough to kill between 10 and 20 humans, or up to two African bull elephants. Smaller doses have been shown to cause seizures, salivation, muscle contractions, dyspnoea and death in mice: the subcutaneous LD50 is just 0.2 µg / kg, although low doses such as 0.01 µg / kg and 0.02 µg / kg may be lethal. Myers et al. estimate that the lethal dose for humans is between 2.0 and 7.5 µg. Synthesis Golden poison frogs appear to rely on the consumption of small insects or other arthropods to synthesize batrachotoxin; frogs kept in captivity fed on commercially available feeder insects will eventually lose their toxicity, and frogs bred in captivity are considered non-toxic. It is not clear which prey species supplies the potent alkaloid that gives golden poison frogs their exceptionally high levels of toxicity, or whether the frogs modify another available toxin to produce a more efficient variant, as do some of the frogs from the genus Dendrobates. Scientists have suggested