Due to the appearance “of the blue dragon (Glaucus atlanticus), and for motives of citizens safety, we have banned all swimming on all of the municipal beaches until a new order,” the Guardamar police force said in a post on Facebook on Wednesday.

The blue dragon, colloquially named for its resemblance to the mythical creatures, is only about 3 centimetres long, but it feeds on venomous animals like the Portuguese man o’ war before recycling and concentrating that venom, allowing it to paralyse prey 300 times its size.

”Contact with this marine animal can be dangerous and provoke painful burns on the skin,” police said, adding that beachgoers should “take extreme caution and avoid direct contact with those that could appear on the sand.”

By Thursday, the ban had been lifted and swimming was allowed, but authorities still urged caution.

The town’s mayor, José Luis Sáez, told the public to notify the authorities if they saw one of the creatures and to avoid touching it, even if wearing gloves.

He advised anyone getting stung to rinse the affected area with saltwater and seek medical attention.

With its sunny climate, rocky cliffs and plethora of beaches, the Mediterranean coastline surrounding Alicante is one of Spain’s tourist hotspots.

Blue dragons are rarely seen in the Mediterranean, being more often found in the temperate and tropical waters of the Atlantic, Pacific and Indian Oceans where they are carried along by ocean currents and the wind.