Ilha da Queimada Grande (Snake Island)

Ilha da Queimada Grande, a 43-hectare island roughly 33 kilometres off the coast of São Paulo state, Brazil, is home to the entire wild population of the golden lancehead pit viper (Bothrops insularis), a species found nowhere else on Earth. Estimates of the island's snake population have varied widely over the decades, from popular claims of "one snake per square metre" to more conservative scientific estimates of a few thousand individuals across the island — still an extraordinarily high density for a venomous snake species, the result of tens of thousands of years of isolation after rising sea levels separated the island from the mainland at the end of the last ice age.

The golden lancehead's venom is reportedly three to five times more potent than that of its mainland relatives, an adaptation researchers attribute to the snake's reliance on birds — which can fly away after a bite unless killed almost instantly — as its primary prey, in the absence of the small mammals available to mainland pit vipers. Local legend holds that the island's last lighthouse keeper and his family were killed by snakes that entered through windows in the 1920s, prompting the Brazilian Navy to automate the lighthouse and ultimately to prohibit civilian access to the island entirely; visits today are permitted only to small numbers of researchers accompanied by medical personnel, studying a species now listed as critically endangered due to historical poaching for the illicit wildlife trade.