Once the mob has finished bullying it, the worm's position has been marked by the fish and the worm loses the element of surprise.
"Concerning their mental capacity, fish are for the most part greatly underestimated," said study co-author Daniel Haag-Wackernagel in a statement. "Research into their behavior in their natural habitats continues to reveal big surprises."
Haag-Wackernagel and his colleagues chalk it all up to survival. The worms typically stay in one location, so the fish risk a too-close encounter, blasting them into retreat, to both save their immediate skins and also to mark "here there be a worm" territory for them to avoid.
The worm, for its part, loses out in another way: Now any other fish nearby that are paying attention also know to steer clear. Tough break.