Ilha da Queimada Grande, known as Snake Island, is a small island off the coast of Brazil with a fearsome reputation. It is densely populated by highly venomous snakes. This concentration of reptiles raises questions about their presence.
The Island’s Identity
Ilha da Queimada Grande is situated approximately 33 kilometers (21 miles) off the coast of São Paulo, Brazil. The island spans about 43 hectares (106 acres), with its terrain varying from exposed rocky areas to lush rainforest. It remains uninhabited by humans.
The Golden Lanceheads
The island is the exclusive habitat of the Golden Lancehead Viper (Bothrops insularis). These pit vipers grow to lengths between 70 to 118 centimeters (28 to 46 inches). Their venom is potent, possessing both hemotoxic and neurotoxic properties, causing severe symptoms like intense local pain, swelling, tissue necrosis, and internal bleeding. The density of these snakes is remarkably high, with estimates ranging from one to five snakes per square meter in some areas, with a total population of 2,000 to 4,000 Golden Lanceheads.
Geological Isolation Theory
The concentrated snake population on the island is attributed to a geological event thousands of years ago. Approximately 11,000 years ago, at the end of the last ice age, global sea levels rose significantly. This rise submerged a land bridge that once connected Ilha da Queimada Grande to the Brazilian mainland. The snake population became isolated on the island, unable to return to the mainland, allowing them to reproduce and thrive without mainland predators.
Evolutionary Specialization
The isolation on Ilha da Queimada Grande led to evolutionary adaptations in the Golden Lancehead Vipers. With no ground-dwelling mammals as prey, the snakes shifted their diet to migratory birds. To effectively hunt birds, their venom evolved to become potent and fast-acting, enabling them to quickly incapacitate prey before the birds could fly away. This specialized venom is considered up to five times stronger than that of their mainland relatives. The Golden Lanceheads also developed more arboreal behaviors, spending time in trees to ambush perching birds.
Restricted Access and Conservation
Today, Ilha da Queimada Grande is off-limits to the public. The Brazilian Navy enforces this ban, primarily to protect humans from the danger posed by the venomous snakes and to conserve the unique ecosystem. Only authorized scientific researchers are granted special permission to visit the island for study. The Golden Lancehead Viper is classified as critically endangered, making the island a protected natural reserve vital for the species’ survival.