Snake Island

Ilha da Queimada Grande, also known as Snake Island, is an island off the coast of Brazil in the Atlantic Ocean. It is administered as part of the municipality of Itanhaém in the State of São Paulo. The island is small in size, only 43 hectares (106 acres), and has a temperate climate. The island’s terrain varies considerably, ranging from bare rock to rainforest.

The island is the only home of the critically endangered, venomous golden lancehead (pit viper), which has a diet of birds. The snakes became trapped on the island when rising sea levels covered up the land that connected it to the mainland. The resulting selection pressure allowed the snakes to adapt to their new environment, increasing rapidly in population and rendering the island dangerous to public visitation.

Queimada Grande is closed to the public in order to protect both people and the snake population. Access is only available to the Brazilian Navy and selected researchers assessed by the Chico Mendes Institute for Biodiversity Conservation, the Brazilian federal conservation unit.

The lancehead genus of snakes is responsible for 90 percent of Brazilian snakebite-related fatalities. The golden lanceheads that occupy Snake Island grow to well over half a meter long, and they possess a powerful fast-acting venom that melts the flesh around their bites. The potent venom of this species evolved due to the need for the snake to quickly incapacitate and kill seabirds that land on the island’s trees before they are able to fly away.

Because there are so many snakes on one island — by some estimates one snake to every square meter — there is competition for resources. On an island ecosystem occupied by hundreds of competitors, the deadly venom of the golden lancehead maximizes its potential to feed and survive. Golden lanceheads are so dangerous that, with the exception of some scientific outfits, the Brazilian Navy has expressly forbidden anyone from landing on the island.

The island was previously thought to have a population of about 430,000 snakes, but recent estimates are much lower. The first systematic study of the population of the golden lancehead found the number to be 2000 to 4000, concentrated almost entirely in the rainforest area of the island.

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