Beaches in the town of Guardamar del Segura, in southeastern Spain , closed earlier this week after the discovery of two venomous sea slugs in the water, local authorities announced.

Due to the appearance “of the blue dragon (Glaucus atlanticus), and for motives of citizenry 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 centimeters (1.2 inches) long, but it feeds on venomous animals like the Portuguese man o’ war before recycling and concentrating that venom, allowing it to paralyze prey 300 times its size.

“Contact with this marine animal can be dangerous and provoke painful b

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