WHERE EACH STEP COULD BE YOUR LAST

The lighthouse keeper and his family were aware of the danger. But one evening when the air in the lighthouse was too muggy to bear, the keeper said good night to his wife and three children and then left the windows open. During the night snakes slithered into the room and bit the sleeping family, who all died in less than an hour. That, at least, is the legend that’s told about Ilha de Queimada Grande, sometimes described as the world’s deadliest island. Two species of snake have evolved on “Snake Island” since rising sea levels isolated it from the Brazilian mainland some 11,000 years ago: the harmless Dipsas albifrons (Sauvage’s snail-eater) and the highly lethal Bothrops insularis, commonly known as the golden lancehead. The island is the only home of this viper, which is one of the world’s deadliest and, at the same time, most endangered snakes. While it has no ground-level predators to fear, it also has no ground-level prey. Other venomous snakes often bite their victims and wait for them to die, but the golden lancehead preys on birds, which quickly fly away. Thus the vipers have evolved to produce an incredibly deadly venom, one that is up to five times more potent than that of mainland snakes and that kills most prey almost instantly (and can melt human flesh). Disease, habitat loss, and poaching (a golden lancehead can fetch up to $30,000) have reduced their population to no more than 4,000, putting them on the Red List of critically endangered species. Altogether, there’s a snake for every square meter of land on the 430,000-square-meter island, which is only visited by scientists who secure the permission of the Brazilian Navy.