Tourists visiting the Costa Blanca in southern Spain have been warned to stay out of the sea following the sighting of poisonous sea slugs known as blue dragons. Swimming has been banned along a seven-mile stretch of coast around the Guardamar del Segura area, just north of Torrevieja. The mayor, Jose Luis Saez, announced the ban via a post on social media, highlighting the danger posed by these creatures and advising the public to keep their distance.

The blue dragon, scientifically known as Glaucus atlanticus, is a type of nudibranch that feasts on the venomous Portuguese man o’ war and other dangerous creatures. According to Australian Geographic, this striking blue creature absorbs the stinging cells from its prey, storing them in concentrated doses to deliver an even more potent sting. Symptoms of a sting can include nausea, pain, vomiting, and acute allergic contact dermatitis.

While sea slugs typically reside on the sea floor, blue dragons are capable of floating on the ocean surface by swallowing air bubbles. This adaptation leaves them vulnerable to strong winds, which can carry them ashore. As of Thursday, the mayor indicated that the warning status had changed to yellow following the conclusion of a special surveillance operation.

Typically measuring around three centimetres or just over one inch in length, these ornate creatures are found in temperate and tropical waters across the Atlantic, Pacific, and Indian Oceans. They have earned a reputation for being equally venomous as the predators they consume, making them a notable threat to swimmers in affected areas.