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Just off the coast of southern Brazil lies the island of Queimada Grande, known as ‘Snake Island’. Covering just 43 hectares (106 acres), this rocky island is home to between 2,000 and 4,000 highly venomous golden lancehead vipers (Bothrops insularis), which can grow to 70cm (just over 2ft). The snakes were trapped there around 11,000 years ago, at the end of the last ice age, when rising sea levels cut them off from the mainland.

No mammals live on the island, so the snakes had no predators to keep their numbers in check, but also very limited prey. With few ground animals to hunt, the snakes became specialists in catching birds that visit the island during their annual migrations.

This diet may explain why their venom is so deadly – whereas most venomous snakes have the luxury of biting their prey and tracking it until it succumbs to the venom, the golden lancehead needs to kill their prey quickly, before the bird has a chance to fly off.

Golden lancehead venom is fast-acting and causes a range of horrifying symptoms, from kidney failure to internal bleeding and tissue death. However, these deadly properties have prompted some researchers to investigate the venom for medicinal uses, such as treating heart disease and blood clots.

Perhaps unsurprisingly, the island is uninhabited (by humans), and the Brazilian Navy has forbidden visitors, except for authorised scientific expeditions. This is as much to protect the snakes as it is to protect unsuspecting tourists – found nowhere else on Earth, golden lanceheads are considered critically endangered. Extremely determined wildlife smugglers make illegal visits to capture the snakes, however, as their potent venom is prized on the black market.

A few brave inhabitants did live there in the early 1900s – tasked with running the lighthouse – but legend has it that the family was killed by snakes, and the lighthouse has since been automated.

The golden lanceheads favour forested areas of the island, where they can hunt their prey. Some estimates suggest that in the forests there may be as many as one lancehead per square meter.

Scientists say that their numbers are decreasing, however, due to habitat loss, disease, illegal poaching and the negative effects of inbreeding in this isolated population. A much smaller, non-venomous snake known as Sauvage’s snail-eater (Dipsas albifrons) also lives on the island.

So, if you ever find yourself stranded on snake island, your best bet is to avoid the forests and stay on the rocky shore, where you’re unlikely to bump into a golden lancehead. If you venture into the forest, watch out for vipers overhead and on the ground.

Edible plants and animals are limited, but you could eat one of the snakes (if you can catch it). Just be sure to remove the head, where the venom glands are located, before you tuck in.

If you suffer a golden lancehead bite, you’ll need to get medical attention very quickly: the venom can kill in under an hour, although only around seven per cent of people die. The island is patrolled by the navy, so a speedy rescue isn’t impossible.