When the mature eels finally reach this safe place, there's no ecstatic coupling to reward them. The males release sperm, the females release roe, then the exhausted parents drift to the bottom to die. No human being has ever seen these eels on the march to the Sargasso, or the spawning there. Some have witnessed the conjugation of conger eels, which reportedly perform a sort of twining tango.
The resulting hatchlings, the leptocephali, drift for at least a year until currents carry them to coastal water. If you put a beaker of fresh water into a salt-water tank containing leptocephali, they'll try to get into the beaker. This suggests it's not just currents taking them to the coast, that they may have a chemical receptor for locating fresh water. They stretch out to eel shape, turn from transparent to gray-brown, and struggle upriver. As brown and slim adolescents, they're elvers. Before they color up, they're known as glass eels—a very expensive delicacy in Spanish cuisine—spaghetti with eyes.
The treks, both ways, worked well for ages. (One more thing that isn't known for sure: There is an ugly rumor that only the females make the trip upstream—that the males loiter in estuaries.) The eels maintained a large population despite their many predators—pike, perch, bass, ospreys, terns, otter, mink, and snapping turtles—until human beings came along with nets and dams.
Though eels have long been thought of as lowly and serpentine, they do have a growing number of human allies. Great Britain has a National Anguilla Club. Energized by a catastrophic drop in European eel numbers, the group has produced a road show—a 90-minute presentation for schools and communities on why it's important to conserve eels. Why indeed? Because they're a critical food source for animals that are easier to love, like otters and water birds, as well as for all those nonelongated fish.
The eels' public image was not helped by their most famous appearance in modern fiction and cinema. In The Tin Drum, Gunter Grass (who won a Nobel prize for this and other work) describes a severed horse's head being pulled from the surf, eels slithering out of its ears and throat. The hero's mother vomits.
Marine biologists do not have that reaction. To John McCosker, chairman of the Department of Aquatic Biology at the California Academy of Sciences, those eels cleaning out the horse's head are "a beautiful sight. Nature doesn't waste anything." Many animals migrate to breed; precisely how and why any of them do it is mysterious. McCosker finds it odd that eels should be so little-studied and so misunderstood. "Because of our intellectual arrogance, we have presumed for centuries that we can understand and control these eels for our benefit," he says. "Yet the Atlantic eels remain unwilling to reveal their migration routes and spawning behavior to us, and I am humbled with the realization of how much we still don't know about them."
Correction, March 1, 2010: The original said that Anguilla, the species name, comes from the Latin word for serpent. Anguilla rostrata is the American eel; Anguilla anguilla is the European eel; both are in the genus Anguilla. (Return to the corrected sentence.)
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