It’s the drag that helps the humble hagfish slime predators so quickly

Courtesy of University of Wisconsin, Madison.

The homely hagfish might look like just your average bottom feeder, but it has a secret weapon: it can unleash a full liter of sticky slime in less than one second. That slime can clog the gills of a predatory shark, for instance, suffocating it. Scientists are unsure just how the hagfish (affectionately known as a 'snot snake') accomplishes this feat, but a new paper in the Journal of the Royal Society Interface suggests that turbulent water flow (specifically, the drag such turbulence produces) is an essential factor.
Scientists have been studying hagfish slime for years because it's such an unusual material. It's not like mucus, which dries out and hardens over time; hagfish slime stays slimy, giving it the consistency of half-solidified gelatin. That's due to long, thread-like fibers in the slime, in addition to the proteins and sugars that make up mucin, the other major component. Those fibers coil up into 'skeins' that resemble balls of yarn. When the hagfish lets loose with a shot of slime, the skeins uncoil and combine with the salt water, blowing up more than 10,000 times its original size.
Yet the precise mechanism for slime deployment is still poorly understood, according to co-author Gaurav Chaudhary of the University of Illinois, Urbana-Champaign. Recent research showed that sea water is essential to the formation of the slime and that hagfish skeins can unravel spontaneously if ions in the sea water mix the adhesives that hold the fibrous threads together in skeins. Chaudhary says that what's missing in this earlier work is taking the fast time scales into account. A 2014 study, for instance, showed that any spontaneous unraveling of the skeins would take several minutes—yet the hagfish deploys its slime in about 0.4 seconds.
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