Ilha da Queimada Grande, often referred to as Snake Island, is a small, isolated landmass located approximately 33 kilometers (20 miles) off the coast of São Paulo, Brazil. This island has gained notoriety for its exceptionally dense population of highly venomous snakes. Its isolation, formed about 11,000 years ago when rising sea levels separated it from the mainland, created a unique environment where a specialized snake species thrived without terrestrial predators. Access to the island is strictly prohibited to the public, with only authorized researchers and the Brazilian Navy permitted to visit.
The Golden Lancehead Viper
The sole snake species inhabiting Ilha da Queimada Grande is the Golden Lancehead Viper, scientifically known as Bothrops insularis. This pit viper is endemic to the island. Its name derives from its pale yellowish-brown color and the distinctive lance-like shape of its head. Adults typically measure between 70 to 90 centimeters (28 to 35 inches) in length, though some can reach up to 118 centimeters (46 inches).
The venom of the Golden Lancehead is particularly potent, highly effective against its specific prey. Chemical analysis indicates its venom is five times more powerful than that of its mainland relative, Bothrops jararaca, and is considered the fastest-acting venom within the Bothrops genus. This rapid action quickly incapacitates prey before it can escape.
Diet: Migratory Birds
The primary, and almost exclusive, diet of adult Golden Lancehead Vipers consists of migratory birds. These birds use Ilha da Queimada Grande as a resting stop during their long journeys along the Brazilian coast. The island lies within established migratory routes, attracting numerous avian species seeking refuge and sustenance.
Examples of bird species that may pass through the island and become prey include various passerine birds. Bird migration patterns along the Brazilian coast suggest a diverse array of avian food sources. The presence of these seasonal visitors dictates the snakes’ feeding patterns and has significantly influenced their evolutionary adaptations.
Hunting Adaptations and Island Ecology
The specialized diet of the Golden Lancehead Viper is a direct result of the island’s unique ecological conditions. Crucially, there are no native mammalian prey species on Ilha da Queimada Grande, forcing the snakes to adapt to an avian diet. This absence of ground-dwelling mammals shaped the vipers’ hunting strategies and physical characteristics.
Golden Lanceheads exhibit arboreal, or tree-dwelling, behaviors, which is a significant adaptation for hunting birds. They spend time coiled on vegetation, waiting to ambush unsuspecting birds. The extreme potency and rapid action of their venom ensure that a struck bird is incapacitated almost instantly, preventing it from flying away and allowing the snake to retain its prey. Unlike some vipers that strike and then track their prey, the Golden Lancehead holds onto its victim after envenomation, a behavior thought to be an adaptation for hunting airborne food sources.