快猫短视频

When a hagfish is attacked by a shark, it spews out a defensive slime that clogs up the predator鈥檚 jaws, allowing the hagfish to escape. The slime rapidly expands in milliseconds, and now we know how.

Gaurav Chaudhary at the University of Illinois at Urbana-Champaign and his colleagues modelled the hydrodynamics of hagfish slime, determining the mathematics that govern the goo. Hagfish slime is made up of mucus cells and 1-micrometre-thick thread-like fibres. Each of these fibres is about 10 to 16 centimetres long, and is twisted into a ball that is a fraction of a millimetre in diameter. It looks a little like a skein of yarn with a single loose thread sticking out of one side. When deployed, such threads fully unravel in under 0.4 seconds to help form a fibrous network for the mucus to stick to.

鈥淪ome experiments have suggested that the threads unravel because seawater dissolves a protective membrane around them, but the timescale doesn鈥檛 work,鈥� Chaudhary says. 鈥淚t happens much faster than that in nature.鈥�

To figure out how the threads unravel so quickly, Chaudhary first tested whether a skein would fully unravel on its own in salt water, or whether it required force pulling on the loose end of the thread. 鈥淥nly when I applied force did it unravel,鈥� he says.

Then he and his team explored the various forces that would pull the loose threads in a shark-eat-hagfish situation.

They modelled a number of scenarios, including one where the loose thread was stuck to a surface but the skein itself was floating free, one where the skein was stuck and the thread was floating free, and one where both were free.

Friction is generated as the skein unravels, but Chaudhary鈥檚 team discovered that this friction is overcome by the drag from seawater acting on the unravelling thread, because the mucus cells wrap around the thread and increase its drag. This mismatch helps explain why the skein unravels so quickly 鈥� but the process is sped up even more if the skein itself is stuck to a surface, such as the shark鈥檚 mouth.

What really helps explain the fast unravelling, though, is if the skeins attach to the shark鈥檚 gills. The drag generated when聽the shark sucks in water over its gills generates even more drag and speeds up the unravelling process.

This help explains why the predator gets such a quick shot of slime to the gills when it attacks a hagfish.