The rhythm of a late August day on the Costa Blanca is a cherished ritual of sun and sea. But on Wednesday, August 20th, 2025, that ritual was abruptly broken. Along the golden coastline of Guardamar del Segura, the familiar green and yellow flags were lowered, and the stark, unambiguous Red Flag was hoisted. The sea was closed.

The cause was not a storm or rough currents, but an invader of mythical beauty and surprising danger: the blue dragon.

The discovery of this tiny, inch-long sea slug, known scientifically as Glaucus atlanticus, triggered a full-scale swimming ban and a wave of fascination and alarm. How could such a small, stunning creature be responsible for major Costa Blanca beach closures at the peak of the tourist season?

This guide provides the full story. We explore the biology of this beautiful killer, explain the science behind its dangerous sting, detail the official response, and investigate the larger ecological reasons for its historic appearance in Spain.

The Incident: How the Blue Dragon Shut Down Guardamar

On the morning of August 20th, 2025, two specimens of the rare blue dragon were discovered on Playa Vivers in Guardamar del Segura. Recognizing the potential danger, the Cruz Roja (Red Cross) lifeguards immediately implemented public safety protocols.

The Bandera Roja (Red Flag) was raised along the entire seven-mile coastline, prohibiting all bathing and water activities. Lifeguards patrolled the shoreline, warning the public of the risk and enforcing the ban. The official warning was clear and absolute: do not touch this animal under any circumstances.

What is the Blue Dragon Sea Slug?

The Glaucus atlanticus is not a jellyfish; it's a species of nudibranch (shell-less mollusc). Unlike its bottom-dwelling relatives, it's a creature of the open ocean, spending its entire life floating upside down on the surface, carried by winds and currents.

Its appearance is a masterpiece of camouflage:

• Blue Side (facing up): Its vibrant blue and silver underbelly faces the sky, blending in with the bright surface of the water to hide from predatory birds.
• Grey Side (facing down): Its dull, silvery-grey back faces into the depths, camouflaging it from fish looking up from below.

This strategy, called countershading, combined with its wing-like appendages (cerata), makes it a perfectly adapted, almost invisible drifter.

Why is the Blue Dragon So Dangerous? The Man o' War Connection

The secret to the blue dragon's danger lies in its diet. Its primary food source is the venomous Portuguese man o' war (Physalia physalis).

While immune to the man o' war's powerful venom itself, the blue dragon does something remarkable. It ingests the most potent, undischarged stinging cells (called nematocysts) from the man o' war's tentacles. It then transports these stolen weapons to the tips of its own feathery appendages and stores them in a concentrated form.

The result: the tiny blue dragon becomes armed with a sting that is often more powerful and painful than the man o' war's own. A single touch can result in an agonizing sting.

What to Do If You Are Stung: First Aid and Safety

The official warnings are not to be taken lightly. If you see a blue dragon, admire it from a safe distance and do not touch it. If you are accidentally stung, follow these crucial first-aid steps:

• Remove any visible tentacles immediately, but not with your bare hands. Use a towel or stick.
• Rinse the area thoroughly with SALTWATER, not fresh water. Fresh water can trigger any remaining stinging cells to fire.
• DO NOT apply vinegar or urine. These are common myths and can make the sting worse.
• Apply a hot pack or immerse the affected area in hot water (as hot as can be tolerated without scalding, approx. 45°C / 113°F) for 20-45 minutes to help neutralize the venom.
• Seek immediate medical attention at the nearest lifeguard post or health centre.

The appearance of rare marine life is fascinating. Learn more about other large visitors in our guide to Whale & Dolphin Watching on the Costa Blanca.

Why Are Blue Dragons Appearing on the Costa Blanca?

The appearance of Glaucus atlanticus in the Mediterranean is an extremely rare event. In fact, a sighting in 2021 was reported as the first in the region in over 300 years. Its return in 2025 suggests a new pattern may be emerging, likely driven by several environmental factors:

• Climate Change & Warming Seas: The Mediterranean is warming faster than the global average. This makes the sea more hospitable to species typically found in warmer, subtropical waters like the Atlantic.
• Shifting Winds and Currents: As a passive drifter, the blue dragon's presence is entirely dependent on where the wind and currents take it. Changes in Atlantic weather patterns can create a "conveyor belt" that pushes these creatures and their food source through the Strait of Gibraltar.
• Presence of Prey: You can't have the predator without the prey. The arrival of blue dragons is almost always preceded by sightings of their food, the Portuguese man o' war. The increased presence of man o' war in the Mediterranean in recent years is a key reason for the dragon's appearance.

The blue dragon is a beautiful but worrying bioindicator—a living signal that our marine ecosystems are undergoing profound changes.

The Impact on a Region Built on Its Beaches

A full beach closure in late August is a major event for the Costa Blanca, a region whose economy is deeply intertwined with tourism. The Guardamar del Segura beach closure caused a significant disruption, affecting local businesses from beach bars (chiringuitos) to watersports rentals.

It highlights a growing challenge for coastal destinations in an era of climate change: balancing public safety and the economic imperatives of tourism with the unpredictable realities of a changing natural world. The incident turned the beach from a place of recreation into a site of natural wonder and cautionary respect, a powerful lesson for locals and tourists alike.

For official beach safety status and warnings in the Valencian Community, always check with the Cruz Roja (Red Cross).

Frequently Asked Questions (FAQ)

Q1: What is a blue dragon?

A1: The blue dragon (Glaucus atlanticus) is a small, inch-long species of sea slug that floats on the surface of the open ocean. It is famous for its vibrant blue and silver colouring and its dangerous sting.

Q2: How dangerous is a blue dragon sting?

A2: A blue dragon's sting is intensely painful and considered more potent than that of its prey, the Portuguese man o' war. It can cause severe pain, skin lesions, nausea, and vomiting. While not typically fatal, it requires immediate medical attention.

Q3: Are there blue dragons in Spain?

A3: The blue dragon is not native to the Mediterranean and is an extremely rare visitor from the Atlantic Ocean. Sightings in 2021 and 2025 on the Costa Blanca are considered significant and unusual ecological events, likely linked to changes in ocean currents and temperatures.

Q4: What should I do if I find a blue dragon on the beach?

A4: DO NOT TOUCH IT. Keep a safe distance, take a photo if you wish, and immediately report the sighting to the nearest lifeguard or by calling the emergency services (112). This will help authorities track their presence and ensure public safety.