Off the shore of Brazil, almost 93 miles away from downtown São Paulo, is Ilha da Queimada Grande, also known as “Snake Island.” The island is untouched by human developers for a very good reason. Researchers estimate that on the island live between one and five snakes per square meter. The snakes live on the many migratory birds (enough to keep the snake density remarkably high) that use the island as a resting point.

“Between one and five snakes per square meter” might not be so terrible if the snakes were, say, two inches long and nonvenomous. The snakes on Queimada Grande, however, are a unique species of pit viper, the golden lancehead. 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. 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.

Locals in the coastal towns near Queimada Grande love to recount two grisly tales of death on Snake Island. In one, a fisherman unwittingly wanders onto the island to pick bananas. Naturally, he is bitten. He manages to return to his boat, where he promptly succumbs to the snake’s venom. He is found sometime later on the boat deck in a great pool of blood.

The other story is of the final lighthouse operator and his family. One night, a handful of snakes enter through a window and attack the man, his wife, and their three children. In a desperate gambit to escape, they flee towards their boat, but they are bitten by snakes on branches overhead.

Marcelo Duarte, a biologist who has visited Snake Island over 20 times, says that the locals’ claim of one to five snakes per square meter is an exaggeration, though perhaps not by much. One snake per square meter is more like it. Not that that should ease one’s mind: At one snake per meter, you’re never more than three feet away from death.