What is the most lethal toxin?
Botulinum toxin
Botulinum toxin (BTX) is a neurotoxic protein produced by the bacterium "Clostridium botulinum" and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromuscular junction and thus causes flaccid paralysis. Infection with the bacterium causes the disease botulism. The toxin is also used commercially in medicine, cosmetics and research.
Botulinum is the most acutely lethal toxin known, with an estimated human median lethal dose (LD) of 1.3–2.1 ng/kg intravenously or intramuscularly and 10–13 ng/kg when inhaled.
Golden poison frog
Thus, the high toxicity of "P. terribilis" appears to be due to the consumption of small insects or other arthropods, and one of these may truly be the most poisonous creature on Earth. Scientists have suggested the crucial insect may be a small beetle from the family Melyridae. At least one species of these beetles produces the same toxin found in "P. terribilis". Their relatives in Colombian rainforests could be the source of the batrachotoxins found in the highly toxic "Phyllobates" frogs of that region.