At first glance, the hagfish—a sinuous, tubular animal with pink-grey skin and a paddle-shaped tail—looks very much like an eel. Naturalists can tell the two apart because hagfish, unlike other fish, lack backbones (and, also, jaws). For everyone else, there’s an even easier method. “Look at the hand holding the fish,” the marine biologist Andrew Thaler once noted. “Is it completely covered in slime? Then, it’s a hagfish.”
Hagfish produce slime the way humans produce opinions—readily, swiftly, defensively, and prodigiously. They slime when attacked or simply when stressed. On July 14, 2017, a truck full of hagfish overturned on an Oregon highway. The animals were destined for South Korea, where they are eaten as a delicacy, but instead, they were strewn across a stretch of Highway 101, covering the road (and at least one unfortunate car) in slime.
Typically, a hagfish will release less than a teaspoon of gunk from the 100 or so slime glands that line its flanks. And in less than half a second, that little amount will expand by 10,000 times—enough to fill a sizable bucket. Reach in, and every move of your hand will drag the water with it. “It doesn’t feel like much at first, as if a spider has built a web underwater,” says Douglas Fudge of Chapman University. But try to lift your hand out, and it’s as if the bucket’s contents are now attached to you.
The slime looks revolting, but it’s also one of nature’s more wondrous substances, unlike anything else that’s been concocted by either evolution or engineers. Fudge, who has been studying its properties for two decades, says that when people first touch it, they are invariably surprised. “It looks like a bunch of mucus that someone just sneezed out of their nose,” he says. “That’s not at all what it’s like.”