If you see this animal, don’t anger it. A hagfish under attack releases thick, clear slime in astonishing quantities. Now scientists have learned that this mucus is a precious resource for a hagfish. After sliming a predator, the fish can take nearly a month to refill its slime glands.

Hagfish live on the ocean bottom, where they’re opportunistic scavengers and hunters. The fish’s potential predators back off quickly after getting a faceful of slime, which clogs their gills. Hagfish, also called slime eels, can free themselves of their own mucus by tying their snaky bodies in a knot and scraping it off. (A highway in Oregon was harder to clean up after a truck full of hagfish crashed there last year.)

The slime itself is a feat of molecular engineering. It comes out of glands that line both sides of the hagfish’s body. The glands hold two kinds of cells: one type is packed with tiny mucus sacs, and cells of the other type each hold one long protein-rich thread, coiled like a skein of yarn. When the hagfish squeezes these cells out of its slime gland, they burst open and mix their contents with seawater. The resulting material expands into a huge volume of slime.

Although scientists have done plenty of research into this substance, they know less about what happens to a slime gland after it’s emptied, write University of Guelph graduate student Sarah Schorno and her coauthors. So the researchers collected hagfish from the east and west coasts of Canada to find out. Pacific and Atlantic hagfish are two different species (Eptatretus stoutii and Myxine glutinosa, respectively).

In the lab, the scientists used mild electrical stimulation to trigger the animals’ slime response, one slime gland at a time. They recorded how many stimulations in a row it took to empty a gland. Then they let the hagfish relax in the lab for the next few weeks, testing them at different time points to see when their slime glands had refilled.

The hagfish emptied their glands quickly; more than half the contents of a gland came out in the first two times it was triggered. But the glands refilled slowly. To the researchers’ surprise, it took three to four weeks for the fish to rebuild their slime supply. Although Pacific hagfish hold a greater volume of slime ingredients in their bodies, both species needed about the same amount of time to recover.

It’s not clear why hagfish need so long to refill their slime glands. Their extremely slow metabolisms might have something to do with it. (In the lab, scientists only had to feed the fish once a month.) But hagfish are thriftier with their mucus than it might seem. They only release slime from the glands that are closest to an attacker. That means that even if those glands need a few weeks to refill, the rest of the hagfish’s body is still ready to slime.

Image: by Vancouver Aquarium