Jellyfish are the world’s most efficient swimmers. They use less energy to travel than any other swimming animal, proportional to their mass. A new study in the journal Nature Communications dives into why jellies are such good (and simultaneously lazy) swimmers: They suction themselves through the water. 

Researchers from the Marine Biological Laboratory in Woods Hole, Massachusetts, Stanford, and elsewhere studied how jellies and lampreys—everyone's favorite bloodsucking jawless fish—move through the water with such ease. The team filled a tank with tiny glass balls in order to study the pressure systems surrounding the sea creatures as they swam, and also cut some of the lampreys’ spines in order to manipulate how the fish were able to swim. 

They found that when the slug-shaped lamprey twists in the water, it creates a kind of mini-tornado with a low-pressure center (just like the eye of a storm). That low-pressure water in turn creates a vacuum which sucks the lamprey forward, toward the higher-pressure water near the fish’s head. Jellyfish swim in a similar manner. This method doesn’t generate a lot of extra energy, allowing the creatures to move more efficiently. Instead of pushing through the water and leaving wakes, like a propeller-driven boat, they slip forward on the strength of their suction. 

The research may eventually inspire better techniques for swimming robots. 

[h/t: Wired]