On an Island Off Brazil, Snakes Rule the Land and Humans Are Banned

There is an island off the coast of Brazil, in the Atlantic Ocean, where humans are banned. Why? Because it is home to thousands of highly venomous snakes that rule the land.

Ilha da Queimada Grande—which is more commonly known as "Snake Island"—is located off the São Paulo coast. It is only about 5,000 feet long and 1,600 feet wide, and at first glance, looks like an idyllic island with forests and surrounded by the crystal blue sea. However it is actually infested with over 2,000 golden lancehead pit vipers.

This particular subspecies of snake is endemic to the island and cannot be found anywhere else in the world. It is also one of the most venomous snakes found in Latin America. Lancehead vipers, a close relative of the island's endemic species found on the mainland, are responsible for around 90 percent of Brazil snake bites.

Ilha da Queimada Grande, Snake Island
Ilha da Queimada Grande, also known as Snake Island, is an island off the coast of Brazil in the Atlantic Ocean. The island is small in size, only 43 hectares (106 acres), and has a temperate climate. The island's terrain varies considerably, ranging from bare rock to rainforest. governomunicipaldeitanhaem/Flickr

The venom of a golden lancehead can kill a person in under an hour unless treated with antivenom right away. And in such a remote location, 90 miles away from land, it is clear why humans are strictly prohibited from setting foot on their home—they would never reach the hospital in time.

However, there are people who have set foot on the treacherous island.

Ligia Amorim is a PhD student at São Paulo state university, in its Program in Biodiversity, and has been visiting the island for research since 2014. Amorim told Newsweek that the island has the second-highest density of snakes in the world, second only to Shedao Island, in China.

"The density of pit vipers on the island is approximately 2,000 individuals, which is quite a number considering the area of ​​the island," she said. "[The snakes'] venom is more potent compared to others of the same genus, but it is more potent in birds, which is her main food."

Amorim said that while landing is strictly prohibited on the island, researchers or the Navy can carry out the landing—only with legal authorization.

"On the island, there is a lighthouse, to avoid collision with boats passing by. The navy maintains this lighthouse annually. In the past, navy lighthouse keepers inhabited the island. So much so that there are remains of buildings there to this day!" Amorim said.

Local legends tell of the fate that awaited the small settlement of people that used to live on the island from 1909 to the 1920s—they were horrifically bitten and killed by a huge fleet of snakes that slithered into their home.

"[The island] is entirely inaccessible from the sea when it is rough, the rocky and steep coast being difficult to reach," Amorim said. "I was never afraid to visit, but I have enormous respect and certain care. I've been to the island over 40 times and I've always been careful. Reporting teams usually take doctors on expeditions, just in case."

When Amorim visits the island, her research group leaves an open call with the city's public health department, "in case something goes wrong."

"If there is a snakebite accident on the island, it is necessary to take the antivenom serum. However, the serum can only be administered by a doctor," she said.

The Golden Lancehead
A picture shows the golden lancehead, the endemic viper on the island. It possesses a potent venom that could kill a person in under an hour. Rafael Benetti

So Why Is This Island so Infested With Snakes?

Amorim said that when ice caps in the area melted, the sea level rose and isolated Queimada Grande from the rest of the world.

"As with other islands on the South and Southeast coast of Brazil, it is estimated that Ilha da Queimada Grande was separated from the mainland at the end of the Pleistocene, 11,000 years ago, at the end of the last glaciation, when the melting of the continental ice caps caused oceanic transgressions and caused the submersion of continental portions," she said.

This geological event caused species that lived on the island to evolve separately from their relatives on the mainland, this creating this different subspecies.

On the island, there are also 68 species of birds–resident and migratory—two species of bats, two species of amphibians, two species of amphisbaenids and three species of lizards. There are no land mammals on the island, meaning the resident snakes are able to thrive and reproduce at rapid rates without inference from potential predators.

In fact, there are so many snakes on the island that some are what scientists refer to as "intersex."

"On the island, there are males, females and individuals called intersex, which are females that have the male copulatory organ, but of different sizes and shapes .The most plausible hypotheses for the appearance of intersex are: (a) eventual mutations that led to the appearance of the intersex phenotype or (b) consequences of inbreeding in the population," Amorim said.

Despite the high density of golden lanceheads on the island, they are actually a critically endangered species.

While able to reproduce freely, their reproductive efficiency is lower than that of its mainland relatives. They are also at risk from illegal removal, by people taking unauthorized trips to the island. They are also subject to wildfires and disease.