What are the dangerous Blue Dragon creatures that led to the closure of Spain’s beaches?

Spain has issued a warning to residents and tourists against swimming at some beaches after rare sea creatures were found along the shore.

The creatures are venomous “Blue Dragons”, often described as “the most beautiful killer in the ocean”.

Authorities in Guardamar del Segura, Alicante on the Costa Blanca, shut down all beaches for a day after the discovery of the Glaucus atlanticus sea slug.

This sea slug survives by feeding on venomous creatures such as the Portuguese man o’war and keeps their stinging cells inside its own body in stronger form.

But what exactly is this creature? How dangerous is it?

Let’s take a look:

What we know about the Blue Dragons

Glaucus atlanticus, better known as the Blue Dragon, is a foraging predator with tentacles that contain strong stinging cells. These are used both to catch prey and to defend itself, according to the US Bureau of Ocean Energy Management.

Easily recognised by its striking dark and light blue stripes, the creature has three pairs of appendages tipped with tendrils.

These spread out like wings, becoming shorter further down the body, which makes the nudibranch look as though it is flying.

It drifts through the ocean, carried by currents and wind, staying afloat with the help of a small gas bubble inside its stomach.

Blue Dragons float on their backs with their patterned blue underside facing upwards. This helps them hide from seabirds flying above, while the silvery grey side facing down blends with the sea surface, making them less visible to fish below.

They are usually found in warm and mild waters of the Atlantic, Pacific and Indian Oceans.

In recent years, Glaucus atlanticus has also appeared along the eastern and southern coasts of Australia, off South Africa, and in 2022 they were spotted washed up on the Texas Gulf Coast.

How dangerous is it?

The sting of the Blue Dragon is as strong as that of the much larger Portuguese man o’ war, which also happens to be one of its prey.

These creatures take in the venom of what they eat and store it at the tips of their finger, using it to protect themselves. If they sense danger, they can release the stinging cells all at once.

Though their appearance may look harmless, almost like something out of a cartoon, they can even turn on each other. Reports say they have sometimes shown cannibalistic behaviour in captivity, according to The Sun UK.

A sting from the shiny Blue Dragon can lead to nausea, pain, vomiting and severe allergic skin reactions.

Jace Tunnell, director of community engagement at the Harte Research Institute for Gulf of Mexico Studies, told BBC, “That’s what makes them so dangerous, since they can release the stinging cells all at one time.”

“It can be three times the intensity as a man-o-war due to that.”

Spain’s advice for tourists

Jose Luis Saez, mayor of Guardamar del Segura, posted on X on Wednesday: “Bathing is prohibited following the appearance on Vivers Beach of two specimens of Glaucus atlanticus, known as the Blue Dragon”, warning people “should stay away from this animal because of its sting”.

A day later, in another post, he said the warning had been reduced to yellow after what he described as a “special surveillance operation”.

Tourists have been urged not to touch the Blue Dragon.

It is not the first time dangerous sea creatures have kept swimmers out of the water in Costa Blanca.

In 2018, visitors were told to avoid the sea after Portuguese men o’ war returned to the area.

An 11-year-old boy had to be taken to the hospital after being stung by one of the jellyfish-like creatures on beaches that were still open along parts of the coastline popular with British tourists.