By NICK CAPOTE and LAUREN EFFRON

One of deadliest snakes in the world rules a speck of land off the coast of Brazil. So many venomous Golden Lancehead pit vipers live there that it has been dubbed, "Snake Island."

The island's lush, green terrain looks like something out of "Jurassic Park" or a Bond villain secret hideout. In reality, the island is uninhabited. The Brazilian government forbids people from visiting it without a permit.

One poisonous bite from the Golden Lancehead pit viper is enough to kill a grown man within a few hours. It's fast-acting venom will burn through flesh and cause its victim to bleed to death.

Rogerio Zacariotti, a researcher with the Cruzeiro Do Sul University in Brazil, travels to "Snake Island" regularly to monitor the Gloden Lancehead population. He is convinced poachers are stealing the snakes from the island and selling them on the black market.

Zacariotti allowed "Nightline Prime" to accompany him and his team on one of his research trips to "Snake Island," where ABC's Dan Harris had some too-close encounters with the deadly snakes. Watch a sneak peek in the video above and catch the full story on "Nightline Prime," Saturday, April 12 at 10 p.m. ET.