An island known for its high density of snakes has captivated public imagination. It serves as a unique natural laboratory, showcasing remarkable adaptations. Its reputation stems from a population of highly venomous serpents.
Ilha da Queimada Grande
Ilha da Queimada Grande, located about 33 kilometers (21 miles) off São Paulo, Brazil, is a small, rocky island covering 43 hectares (106 acres). Its terrain ranges from bare rock to rainforest. The island remains uninhabited by humans, and access is strictly restricted by the Brazilian government for safety and conservation.
The island is the sole natural habitat for the Golden Lancehead Viper (Bothrops insularis), a highly venomous pit viper. This snake is considered one of the most venomous in the world. Its venom is potent, estimated to be up to five times stronger than that of its mainland relatives, an adaptation to quickly incapacitate prey.
Counting the Snakes
An exact count of the snake population on Ilha da Queimada Grande is not possible due to the challenging terrain and secretive vipers. Estimates suggest the Golden Lancehead Viper population ranges from 2,000 to 4,000 individuals. In some areas, particularly within the forest, density can be as high as one snake per square meter.
These population figures are derived from observational studies and density calculations. While older, sensational estimates suggested populations as high as 400,000 or even one snake per square meter across the entire island, these numbers are exaggerated. The island’s limited resources cannot sustain such a large number of snakes, indicating current estimates provide a more realistic picture of this density.
Why So Many Snakes
The high snake population on Ilha da Queimada Grande is a result of its unique ecological history. Approximately 11,000 years ago, rising sea levels separated the landmass from mainland Brazil, trapping snakes on the island. This geographical isolation prevented ground predators, allowing the snake population to flourish without natural threats.
The island also provides an abundant food source for the vipers: migratory birds. These birds use the island as a resting stop during their long flights. The Golden Lancehead Viper’s potent venom evolved as an adaptation to this avian diet, ensuring bitten birds are quickly incapacitated before they can escape, securing the meal.