Brazil Has an Island the Navy Will Not Let You Visit

Ilha da Queimada Grande is a wedge-shaped piece of granite covered in Atlantic Forest, about 43 hectares — 106 acres — sitting 33 kilometres off the coast of São Paulo state in Brazil. It is closed to the public. The Brazilian Navy maintains a small lighthouse on it, automated since 1925, and otherwise nobody lives there. The reason is the snakes.

When sea levels rose at the end of the last ice age, an isolated population of mainland pit vipers found itself stranded on the new island. Cut off from terrestrial prey, they took to climbing trees to ambush migratory birds. Over thousands of generations they evolved into a separate species, Bothrops insularis, the golden lancehead — small, pale orange, and packing venom three to five times more potent than that of their mainland cousins. They needed it: a bird that flies a few seconds after a slow-acting bite is gone forever, so the snakes' venom kills almost on impact.

The popular figure of "one snake per square metre" comes from older surveys. The first careful systematic count, by herpetologists at Instituto Butantan in São Paulo, put the actual population at 2,000 to 4,000 individuals, concentrated almost entirely in the rainforest interior. The species is critically endangered: the island is small, the gene pool is tiny, and illegal collection by snake smugglers (a single golden lancehead can sell for tens of thousands of dollars on the black market) keeps thinning it.

The Navy issues access permits only to scientific teams, and those visits require a doctor on the boat. The legend that an entire family of lighthouse keepers was killed in their beds by snakes pouring through the windows is unsubstantiated; the lighthouse was already automated. The reason for the access ban is mostly the other direction: keep the snakes alive, and the rare unlucky tourist out.