Ilha da Queimada Grande, known colloquially as “Snake Island” is an outcropping of ocean rock that is about 43 hectares (106 acres) in area, and most people – including decision makers in the Brazilian government – consider it unusually treacherous. This is due almost entirely to the large population of snakes: the golden spearhead.
An old Brazilian story suggests that Ilha da Queimada Grande’s snake population was a direct result of some resourceful pirates and their ploy to discourage people from finding their buried loot. However, the real reason for the island’s unique population is a little less fantastic.
The evolution of the Golden Spearhead Serpent
The Golden Spearhead is a highly venomous viper. And comprehensive survey conducted in 2008 concluded that Ilha da Queimada Grande is probably home to between 2,000 and 4,000 of these vipers. Although they are relatively abundant on the island, the fact that they only exist here means that they are taken into account critically endangered on the IUCN Red List.
“Island populations tend to be less genetically diverse because they are more likely to cross over tight spots [low population numbers], which reduce genetic diversity. Genetic diversity is important,” he explains Robert Aldridge, professor of biology at Saint Louis University.
About 11,000 years ago, during a period known as the early Holocene, global sea levels have risen by about 60 meters as a result of the breakup of ice masses and the breakup of coastal ice streams. This uplift caused Ilha da Queimada Grande to separate from mainland Brazil, meaning its snakes took a different evolutionary path than their mainland cousins.
“[The golden lancehead] is an insular species that seems most closely related to the continental form – the [Bothrops jararaca] — and now it’s isolated from that species,” explains Stephen P. Mackey, a professor who specializes in evolution, ecology and toxinology at the University of Northern Colorado’s School of Biological Sciences.
Because of the island’s small habitat and the abundance of birds — which prey on these snakes — the snakes’ size, venom and color pattern have evolved differently, according to Mackessy.
“If it was transported to similar islands in the area, it would probably thrive, but it just hasn’t gotten there,” says McKessy.
Are snakes deadly to humans?
Mackesy says the golden lancehead is undoubtedly a threat to the island’s birds – but what about humans?
“Nothing I’ve seen suggests that the golden spearhead poses any greater risk to humans than many other species Bothrops pit snakes – many of which grow significantly larger,” says Mackessy. “The idea that it’s extremely deadly is most likely a myth.”
There is no official record of a golden lancer biting a human. But some experts predict that the snake’s hemotoxic venom may cause degeneration of organsheart attack, muscle paralysis or, in the worst case, death of a victim.
Felipe Graziotin, a scientist at the Instituto Butantan, a Brazilian biological research center, believes that the viper’s venom can affect the human body in the same way as the species Bothrops.
“Yes, they are poisonous, potentially fatally poisonous to a person,” Mackessy adds, “but […] with a little caution, one can easily navigate even the ‘serpentiest’ areas of Snake Island.”
Should people visit the island?
While traveling to the island doesn’t necessarily mean danger, Mackesy doesn’t think tourists should visit it anytime soon.
“I really don’t think there’s any reason for tourists to have access to the island,” Mackesy says. The habitat would not threaten a trained herpetologistbut there could be accidents for the general population, according to Mackesy.
“I extract venom from a lot of snakes and have been doing it for over 35 years without incident, but it’s still something I would avoid if there was a viable alternative because it involves a level of risk,” says Mackessy.
However, Grazziotin believes that tourism may ultimately play a role in the long-term survival of the golden javelin.
“A smart way to protect these islands [and animals] would be to get local people involved, promoting tourism and proper knowledge of the incredible biodiversity we have,” he says.