Known as Snake Island, the viper-infested Ilha da Queimada Grande sits in the Atlantic Ocean about 90 miles off the coast of southeastern Brazil. Legend has it that the last fisherman who strayed too close to the shores of Snake Island was found days later adrift in his own boat, lying lifeless in a pool of blood. This mysterious island, also known as Ilha da Queimada Grande, is so dangerous that Brazil has made it illegal for anyone to visit. And the danger on the island comes in the form of the golden lancehead pit vipers – one of the deadliest snakes in the world.

The lanceheads can grow to be over a foot-and-a-half long and it’s estimated that there are between 2,000 and 4,000 of them on Snake Island. The lanceheads are so venomous that a human bitten by one could be dead within an hour. The lanceheads can grow to be over a foot-and-a-half long and it’s estimated that there are between 2,000 and 4,000 of them on Snake Island. The lanceheads are so venomous that a human bitten by one could be dead within an hour.

In reality, the vipers’ presence is the result of rising sea levels – a less exciting origin story than paranoid pirates to be sure, but still interesting. Snake Island used to be part of Brazil’s mainland, but when sea levels rose over 10,000 years ago, it separated the landmass and turned it into an island.

The animals that wound up isolated on Queimada Grande evolved differently from those on the mainland over the course of millennia, the golden lanceheads in particular. Since the island vipers had no prey but birds, they evolved to have extra-potent venom so that they could almost immediately kill any bird. 

Lancehead snakes, which are the golden lanceheads’ mainland cousins, are responsible for 90 percent of all snake bites in Brazil. A bite from their golden relatives, whose venom is up to five times more potent, is less likely to actually happen due to their island isolation. However, such an encounter is far more likely to be lethal if it does happen.