Yanni Vortman

Scientists have known many animals have this sixth sense for decades, but they still don't know how they do it.

As in, we know eyes are used for seeing, noses for smelling, ears for hearing, but it's unclear what organ or sensor is detecting gravitational fields.

Behavioral ecologist Yanni Vortman is the author of the new study published in the journal Biology Letters.

And he says earthworms are easier to study because they don't have eyes or ears and they're easy to acquire.

Nate Rott, NPR News.