These animals employ so-called batrachotoxins (BTXs), which are secreted through the skin, as protection against parasites and predators. Because the skin of frogs raised in captivity lacks detectable amounts of BTXs, researchers surmised that the creatures must obtain the poison from their food, though no insect or plant had been found to contain BTXs. Now John P. Dumbacher of the California Academy of Sciences and his colleagues have discovered in New Guinea a type of beetle that harbors high levels of the chemical. Local villagers suggested beetles of the genus Choresine as a potential source, because contact with them causes tingling and numbness.
The researchers collected nearly 400 bugs and identified a variety of BTXs, some of which had not previously been identified. Because New Guinea's passerine birds feed on insects, including beetles, the authors posit that the bugs are a direct source of the chemicals in the toxic birds. They further note that close relatives of Choresine are common in the rainforests of Colombia and may thus supply the local poison-dart frogs with their lethal power.