About 33 kilometres off the coast of São Paulo state lies Ilha da Queimada Grande, better known as Snake Island. This rocky, forested speck in the Atlantic is the only place on Earth where the golden lancehead, Bothrops insularis, lives in the wild. Today the island is closed to the public and reserved for research.

Aerial view of Ilha da Queimada Grande, Snake Island, off the Brazilian coast
Ilha da Queimada Grande from the air. Photo: Wikimedia Commons.

Ilha da Queimada Grande at a glance

  • Location: Atlantic Ocean, about 33 km off the São Paulo coast, administered by the municipality of Itanhaém
  • Area: about 43 hectares (0.43 km²)
  • Highest point: 206 metres above sea level
  • Famous resident: the golden lancehead, found nowhere else
  • Access: closed to the public by the Brazilian Navy

The name means "big burnt island". Queimada refers to the fires once set to clear the forest for a banana plantation. A lighthouse was built in 1909 to warn ships away from the rocks; it was automated in the 1920s, and the last human inhabitants left at that time.

How the golden lancehead came to live here

At the end of the last ice age, rising seas cut the island off from the mainland, and a population of lanceheads was trapped on it. With no mammals to hunt, the snakes adapted to the prey that was available: birds. Golden lanceheads feed mostly on perching birds, especially migrants that stop on the island to rest, and they also eat lizards. Young snakes mainly eat invertebrates.

Researcher observing a snake among the trees of Snake Island – photo by Mark Moffett
A researcher at work among the island's trees. Photo: Mark Moffett.

The species was described scientifically by the Brazilian herpetologist Amaral in the early 1920s. Adults usually measure 70 to 90 centimetres, with a recorded maximum of 118 cm, and are a pale yellowish brown with darker blotches, which gives them their golden name.

Venom built for birds

The golden lancehead's venom evolved for its island prey, and it is the fastest-acting venom in the genus Bothrops. Laboratory analysis suggests it is around five times as potent as that of its mainland relative, the jararaca (Bothrops jararaca), and it is especially effective against birds and other non-mammal prey.

The island's snake population was once said to be as high as 430,000. Systematic surveys tell a very different story: the first study estimated 2,000 to 4,000 snakes, and a 2021 estimate based on 2015 surveys put the number at roughly 2,400 to 2,900.

A critically endangered snake

For all its fearsome reputation, the golden lancehead is listed as Critically Endangered by the IUCN. Its whole world is a single small island, and the threats are real:

  • Loss of vegetation, from past fires and from clearing around the lighthouse
  • Illegal collection for the wildlife trade, with specimens reportedly offered for up to US$30,000 in 2008
  • Heavy inbreeding, which has produced many sterile intersex snakes and reduced female fertility
  • Fewer migrating birds, linked to deforestation on the mainland

A 2020 conservation genetics study examined the species' genetic variation and what it means for managing such a small, isolated population.

Golden lancehead snake on Ilha da Queimada Grande – photo from Itanhaem.sp.gov.br
Photo: Itanhaem.sp.gov.br

Can you visit Snake Island?

No. The Brazilian Navy has closed the island to the public, and only Navy personnel and researchers approved by ICMBio, the Chico Mendes Institute for Biodiversity Conservation, may land. The ban protects both visitors and the snakes.

The best way to learn about the golden lancehead is through Brazil's research institutions and museums, where the species is studied.

Our Guelta d’Archei article explores another unusual wildlife setting with serious limits on travel. Jellyfish Lake in Palau shows how a specialised habitat shapes the way visitors behave.

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