These eel-like creatures use their flaccid, squishy skin to survive shark attacks

Hagfish are jawless, eel-like creatures that are known to spray huge quantities of goo when attacked. Now, scientists have found another defense mechanism that protects these slimy monsters: their flaccid, squishy skin.

Researchers attached mako shark teeth to a guillotine to replicate how a real shark would bite down on a hagfish. The hagfish’s loose skin allowed the shark tooth to cut through skin but never through the underlying muscle. That allows hagfish to squish away, escaping shark attacks relatively unharmed, according to a study published this week in the Journal of Royal Society Interface.

Hagfish had their moment of fame earlier this year, when a truck transporting 7,500 pounds of the eel-like creatures tipped over, spreading unimaginable amounts of car-coating mucus all over an Oregon roadway. The slime is made of a sugar-coated protein called mucin and coiled-up spools of thread that are kind of like spider silk. When a hagfish is attacked, it releases the slimy mesh to protect itself. In fact, the goo clogs the gills of the predator, which then releases the hagfish to save its own dear life.

In a video published by researchers in 2011, a hagfish was observed spraying the slime onto a biting shark in New Zealand. The shark looks like it’s chocking on a cloud of snot, which allows the hagfish to swim away unscathed. So after seeing the video, a team of researchers in Canada and the US wanted to know: how exactly can hagfish survive shark attacks? “It was a weird observation that this animal could be bit by a shark and then swim away apparently unharmed except for one puncture mark,” says study co-author Sarah Boggett, a high school teacher and researcher at the Department of Integrative Biology at the University of Guelph.

First, the researchers put hagfish skin — which has three layers and no scales — in a machine that pokes a pin through it to measure the force needed to puncture it. Compared to 21 other species of fish, like rainbow trout and great sculpin, the hagfish wasn’t found to have a particularly tough skin. But, the secret lay somewhere else: in how flabby the skin is.

Hagfish skin is attached to the animal’s body in only two spots: the middle of its back and its sides, where the slime glands are located. So Boggett injected a solution under the skin of several dead hagfish to check how much space there is between the body and the skin. The answer is mind-boggling: in Pacific hagfish, that extra space can contain about 46 percent of the animal’s own body volume. If you inject enough fluid so that the skin starts stretching and the hagfish starts leaking, you could fit over 100 percent of its body volume in there. That means you could essentially fit two hagfish within the skin of one.

The researchers then attached mako shark teeth to a custom-made guillotine, so that the teeth could be driven into dead hagfish with the same force they would in real life. The loose skin functioned as a flaccid, squishy armor: the fangs could puncture the skin but not the underlying muscles, reducing the damage of a shark bite.

So, mystery solved. Now we know that flabby skin isn’t bad for everyone. It can save lives.