Experts used to believe the yellow-bellied sea snake was the only snake to live entirely in the ocean. While other sea-dwelling snakes laid their eggs on land, they stayed and gave birth in the open water to live young. But yellow-bellied snakes, like all animals, need water to survive. They can't, as previously thought and written so in text books, filter the salt from the sea (via a special gland on their tongue) and drink from their surroundings, National Geographic reported.
Instead, yellow-bellied snakes rely on freshwater, even though they spend all their time in the ocean. Harvey Lillywhite, who's been studying sea snakes for decades at his post at the University of Florida, wondered if they might be accessing deep springs. Such sites, however, are far-ranging. Plus, he hadn't found yellow-bellieds congregating around them. Eventually, he realized it was rainwater.
Before rain mixes with the ocean's salt, it sits uncontaminated at the surface long enough for snakes to get in their licks. Because yellow-bellied are also believed to be specially adapted to withstand long droughts, they're able to survive on rainwater alone. The trait is necessary at sea during drought season. In fact, a prolonged drought affecting Northern Australia is thought to be the reason for the mysterious exctinction of numerous species of sea snake.
Lillywhite's theory is confirmed by lab results. In addition to yellow-bellied snakes, he's tested other types of sea snakes, none which have ever drank sea-water. Even the thirsty ones will refuse or choose freshwater instead, if that is an option.
"We've looked at hundreds," he told Nat Geo. "No sea snake we've observed has drunk any seawater. If the snake drinks fresh water, it's thirsty," says Lillywhite. "If it's thirsty, it's dehydrated, and if it's dehydrated, it's not doing what the textbooks said."
