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Blue Glaucus Glaucus atlanticus

Glaucus Atlanticus,aka. The “Blue Dragon”

Glaucus Atlanticus,aka. The “Blue Dragon”

Glaucus Atlanticus
Glaucus Atlanticus

The Blue Dragon, The World’s Most Beautiful – And Deadly – Slug

Like most nudibranchs, this species incorporates toxic chemicals or stinging cells from its prey into its own skin.

This ability provides the blue glaucus with a defense mechanism against predation.

Despite its impressive arsenal of defense tactics, the blue glaucus rarely reaches more than 3 centimeters long. And, unlike most benthic nudibranchs, this species lives throughout the entire water column. An air bubble stored in its stomach keeps the nudibranch afloat.

The creature often floats on its backside, showing its brightly colored underbelly to airborne predators.

The bright blue color acts as camouflage against the backdrop of ocean waves while the animal’s grayish backside blends with the bright sea surface, concealing it from predators below. This is an example of a phenomenon known as countershading, helping the creature to avoid both flying and swimming predators while floating in open water. 

Glaucus atlanticus can be just as dangerous on the beach. After they’ve fed on poisonous jellyfish, they have the ability to concentrate that poison within their bodies and unleash a sting more powerful than that of the jellyfish they ate.

Unsuspecting beachgoers can sometimes find themselves on the painful end of that sting.

Glaucus atlanticus sightings are rare, but far from unheard of, on the shores of Australia. This isn’t surprising given the creature’s preference for the warmer waters of the Pacific and Indian oceans.

The blue gaucus, like all nudibranchs, is hermaphroditic — each individual produces both eggs and sperm. An individual cannot fertilize its own eggs, however, and pairs still must mate. Long, spiral-shaped eggs are produced by both male and female, and often float freely in the water or stick to nearby surfaces.

Like most small marine invertebrates, little is known about the conservation status of the blue glaucus, especially given the species’ pelagic lifestyle in the open ocean.

Maximum size:  35 mm


Circumglobal in temperate and tropical waters