Hagfish: The world's slimiest creatures - Noah R. Bressman and Douglas Fudge

As the truck screeched to a halt, one of its containers slid off, hit an approaching Prius, and spilled its contents. Those contents happened to be thousands of kilograms of live hagfish, also known as slime eels. The result of this 2017 car accident was an absolute mess: the highway was littered with wriggling fish and coated in a thick slime that took the fire department 7 hours to clear.

Astonishingly good looks aside, the standout strength of all hagfishes is their slime. In fact, they’re probably Earth’s slimiest animals. But why be so slimy? Watch and learn. This hagfish has detected a dead fish using its keen sense of smell and the tastebud-like organs dotting its skin. Revealing imposing rows of toothlike structures, it takes the first bite.

A shark glides on to the scene and suddenly lunges. Being caught in the shark’s powerful jaws may seem like a guaranteed death sentence, but the hagfish has some tricks up its sleeve. The shark’s teeth clench down, but there are no bones to crush—only flexible cartilage. And because the hagfish’s skin is so loosely attached to the rest of its body, the pressure from the bite causes the hagfish’s essential organs to slip out of the way, avoiding damage. This is where being a noodle in a baggy wetsuit really pays off.

Meanwhile, the hagfish also actively repels the shark by spewing a stupendous supply of slime. Around a hundred slime glands line each side of the hagfish’s body. Within them are mucus and thread cells. The mucus cells are packed with hundreds of vesicles of condensed mucus, while each thread cell contains an intricately coiled protein fiber. The hagfish contracts the muscles surrounding some of its slime glands, causing the cells to eject their contents into the seawater.

In a fraction of a second, the mucus vesicles swell and burst, and the protein fibers unravel. Together, they expand to 10,000 times their original volume, instantly creating liters of slime. Because the substance is composed of mucus and reinforced with numerous superfine and strong silk-like fibers, the slime is incredibly soft yet tough. It lodges in the shark’s delicate gills, and as the shark chokes and tries to clear the slime, it releases the hagfish.

Now, the hagfish is free from the jaws of death. But it’s in a dilemma of its own doing, trapped in a cloud of its own suffocating slime. So what does it do? Well, it ties itself in a knot, of course. Starting at its tail and passing its body through, the hagfish effectively wipes away its own slime. Apparently unfazed by the whole encounter, it returns to its meal.

When it gets to a tougher part of the carcass... Voila! The hagfish ties itself in yet another knot to gain leverage and yank off the meat. The hagfish’s slime is so remarkable that people are trying to emulate it. Currently, a lot of athletic and safety gear is made from non-renewable petroleum-based fibers. But hagfish slime threads rival the properties of materials like nylon.

And fibers modeled after those in hagfish slime may present a much more sustainable alternative. Meanwhile, hagfish slime is also being explored in military contexts as a non-lethal weapon that could be used to stop boats by sliming up their propellers. In addition to mastering the art of slime and knot-tying, hagfish have four little hearts and can survive 36 hours without oxygen unscathed.

Oh, and they also clean the seafloor and cycle essential nutrients in the deep sea. Proto-hagfish were navigating the ocean’s depths more than 300 million years ago—before dinosaurs roamed and back when Pangea was still a thing. Having persisted through multiple mass extinction events, hagfish have just about seen it all. And it would appear that they’re still having a wonderful slime.