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