‘Blue Dragon’ Sea Slugs May Look Pretty but Deliver Potent Sting Because of What They Eat

(Sahara Frost/Shutterstock)

The fantastically named “blue dragon” is an ocean dwelling animal which looks as impressive as it sounds. They are in fact a type of  sea slug (nudibranch), but these flashy slugs boast an incredible defense mechanism that sets them apart from their garden-variety cousins.

The blue dragon—Glaucus atlanticus—has been known to scientists for over 300 years. Often ending up in rocky pools between high tides, their beauty belies a fearsome weapon.

To avoid predators, this sea slug ingests the stinging cells of a Portuguese man o' war (or bluebottle), and cleverly transfers the sting to the tips of its cerata, its wing-like appendages on the sides of its body.

The ingested cells then become the blue dragon’s own formidable defense.

(Sahara Frost/Shutterstock)

Portuguese man o' war (NFKenyon/Shutterstock)

“Ever since I can remember I’ve seen them washed up on local beaches,” said sea slug expert Steve Smith, director of the National Marine Science Centre at Southern Cross University in Lismore, Australia, to Australian Geographic. “You can’t really predict when it’s going to occur. It depends on what the aggregations are like offshore and how long the wind blows for.”

Many species of sea slug stick to the ocean floor, yet blue dragons swallow air bubbles, allowing their flat bodies to float on the surface of the water, though upside-down, and employ countershading, similar to sharks, to camouflage their bodies—a second defensive mechanism.

The blue dragon’s dark upper aspect allows it to blend into the ocean when seen from above. Its silver-colored underside blends into the color of the sky when seen from below.

(Sahara Frost/Shutterstock)

(Katherine Wallis/Shutterstock)

Free-floating in both temperate and tropical waters, blue dragons can be found in the Atlantic, Pacific, and Indian oceans, explains Treehugger. They are hermaphroditic, laying around 20 eggs at a time. And while only 1.2 inches (3 cm) in length, serrated teeth allow them to feast on creatures many times their size, making their name a fitting one.

Eagle-eyed beachgoers may spot blue dragons more often than other sea slugs, as their tendency to float exposes them to winds that wash them ashore. And their habit of forming in large numbers, or “blue fleets,” on the ocean surface draws considerable attention.

It may be inadvisable to pick them up; the blue dragon has the capacity to deliver a sting equal in potency to that of a bluebottle, even long after the blue dragon dies.

(Imtorn/CC BY-SA 3.0)

Yet, Smith claims he has never been stung. “They may have the capacity to sting, but it doesn’t mean they’re going to do it every time,” he shared.

Thanks to amateur photography and the blue dragon’s striking look, new sightings are frequently reported. The blue slugs showed up in Taiwan in 2017. In 2020, they made appearances in both Texas and Cape Town, South Africa.

Smith’s citizen scientist program Sea Slug Census benefits hugely from this data. “The blue dragon is really one of those nudibranchs that showcase beauty, pattern, and adaption,” he praised.

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