It’s time for bed, and what better way to ensure a comfortable
sleep than snuggling into a cocoon of your own mucus? Humans
could probably think of some alternatives, but for many coral
reef fish, mucus sleeping bags are all part of a good night’s
rest. Many species of parrotfish and wrasse belch out their own
cocoons every night, covering themselves in under an hour. And
Alexandra Grutter from the University of Queensland thinks she
knows why – the mucus deters vampires. There are many possible
explanations for the cocoons: they’re an early warning system;
they act as a dust sheet; they protect the fish from DNA damage
caused by sunlight; the list goes on. The most popular theory is
that the cocoons protect the fish from predators. It dates back
to 1959 when Howard Winn and John Bardach found that three
species of mucus-weavers are less often eaten by moray eels than
a fourth species that sleeps uncovered. But the duo never
considered other differences between the four species and they
still found that the e