The existing dead sample was assumed to be a labelling error and the snake was largely struck from taxonomic registries.

But Daniel Mulcahy, a researcher for the National Museum of Natural History in Washington, suspected it might still exist. He and Juan Martinez Gomez of Mexico's Ecology Institute set out to find it.

Martinez Gomez, an expert on the Revillagigedo Islands, noted the islands change a lot from season to season, so they timed the expedition last May to replicate Beebe's steps as they looked for the snake, which blends in with the island's rock formations and is largely active at night. And they used Beebe's original field notes as a guide.

"Basically, following those directions, we essentially put ourselves in his place," Martinez Gomez said.

One of his graduate students, Juan Alberto Cervantes, was the first to spot one of the snakes for the first time since 1936.

The researchers performed DNA analysis to establish the long, dark spotted snake as its own species and see where it had come from.