Tourists have been banned from going into the water along an entire seven-mile stretch of Spain’s Costa Blanca due to an invasion of venomous “blue dragons”.
The rare sea creatures have a potentially-fatal sting and are dubbed “the most beautiful killer in the ocean”.
Reg flags went up on beaches in Guardamar del Segura just north of Torrevieja following the appearance of slugs also known as Glaucus atlanticus.
Just over an inch long, it has a sting as powerful as the much larger Portuguese man o’ war and also preys on them.
Despite the ban, beaches remained packed with holidaymakers although with far fewer bathers in the water.
Local mayor Jose Luis Saez wrote on X, formerly Twitter: “Red flag on the beaches of Guardamar.
“Bathing is prohibited following the appearance on Vivers Beach of two specimens of Glaucus atlanticus, known as the Blue Dragon.”
According to Mr Sáez, the ban will remain on the beach up to 24 hours, depending on the evolution of the situation.
Bandera ROJA en las playas de Guardamar PROHIBIDO el BAÑO tras la aparición en Playa Vivers de dos ejemplares de Glaucus atlanticus, conocido como Dragón Azul. pic.twitter.com/Ksy21uADmO
— José Luis Sáez (@JoseLSaezPastor) August 20, 2025
He added: “We remind people that despite its bright and striking colour and its small 1.5 inch size, they should stay away from this animal because of its sting.
“Guardamar del Segura Town Hall has launched a preventive operation to detect possible specimens carried by ocean currents.
“Town hall workers are closely following the evolution of the situation and will inform people about the different measures to be taken.
“If you see one of these creatures don’t touch it, even with gloves on, alert lifeguards and other authorities.
“If you get stung, wash the area affected with salt water and head to your nearest first aid point or health centre.
“These creatures are poisonous and their stings can cause nausea, pain and vomiting.
“For the time being and until further notice, bathing in the sea is prohibited.”
Iin 2018, experts warned people not to touch the mini monsters after large numbers swarmed the coast of Sydney, Australia.
In April, Spain was hit by a spectacular invasion of small blue jellyfish.
