20 Animal Journeys That Still Defy Explanation

For centuries, eels have made scientists feel like detectives who arrived just a little too late. European and American eels grow in rivers, lakes, and coastal waters, then make long journeys toward the Sargasso Sea, where spawning is believed to occur. Larvae have been found there, which strongly supports the location, but adult eels spawning in the wild have remained famously unseen. That missing scene gives the whole life cycle an old-fashioned mystery, the kind that once puzzled naturalists and still fascinates modern researchers with better tools.