While some people might find these slimy creatures at the beach very exciting, a number of species are poisonous; some tropical species are even among the most toxic animals on earth. Even worse, rising water temperatures, ocean acidification and overfishing seem to favor the jellyfish blooms. More and more often, they appear in huge swarms, which have already destroyed whole fish farms on European coasts and blocked cooling systems of power stations near the coast. Can we find a solution to this emerging environmental threat?