Most poisonous salamander

The world’s most poisonous salamanders (Caudata) are the Pacific newts (genus Taricha), whose skin, muscles and blood contain tetrodotoxin (TTX), a highly toxic and powerful nerve poison. The rough-skinned newt (T. granulosa) is deemed particularly dangerous as a single individual can harbour as much as 14 mg (0.0005 oz) of TTX; less than 1 mg could kill a typical adult man if ingested. Although the newt itself is immune to its effects, one tiny drop of this substance will kill several thousand mice and there are documented cases of human deaths. These amphibians are native to ponds, slow-moving streams, ditches and wetland areas on the western coast of the USA, Canada and Mexico.

Tetrodotoxin is the same toxic substance found in pufferfish, the most poisonous fish, and the blue-ringed octopus, the most poisonous mollusc, and has an LD50 (lethal dose in 50% of cases) in humans of just 10.2 μg/kg.

A number of predators, including garter snakes (genus Thamnophis), appear to have evolved an immunity to the poison. As a result, certain populations of newts seem to be increasing their toxicity over time in an attempt to counteract this threat. Studies indicate that the newts derive their toxicity from bacteria, such as Pseudomonas, that dwell on their skin.

Other salamanders have also been found to have TTX in their bodies as a means of self-defence, including examples from the genera Triturus and Cynops, but generally not in such high quantities or as potent as that found in Taricha species. A number of frogs and toads also harbour this toxin.