Blue Dragon
A thumb-sized sea slug that floats upside down, eats the Man-o'-War, and steals its weapons
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Superpower
The blue dragon eats the Portuguese Man-o'-War — one of the ocean's most venomous animals — and doesn't digest the stinging cells (nematocysts). Instead, it stores them in concentrated clusters in the tips of its finger-like appendages (cerata). The blue dragon becomes more dangerous to touch than the Man-o'-War itself, because the stingers are concentrated rather than spread across long tentacles. A beachgoer who picks up this beautiful 3cm slug may receive a more severe sting than if they'd touched the jellyfish directly.
Overview
This tiny nudibranch floats at the ocean surface, upside down, suspended by a bubble of swallowed air in its stomach. It drifts with the wind across all tropical and subtropical oceans, preying on whatever surface-floating animals it encounters — By-the-Wind Sailors, Portuguese Man-o'-War, and other siphonophores. Its silver-blue coloration is counter-shading: the silver underside (facing upward toward sky-watching birds) blends with the ocean surface; the blue side (facing downward) blends with open water when seen by fish below. It is simultaneously camouflaged from threats above and below.
Found in
Open ocean surface worldwide in tropical and subtropical waters. Also found in the Mediterranean. Often washed ashore in large numbers after storms — particularly on beaches in South Africa, Australia, and the Gulf Coast.
Things worth knowing
- 1
The blue dragon is a simultaneous hermaphrodite — every individual has both male and female reproductive organs at the same time, and any two individuals that meet can mate.
- 2
When food is scarce, blue dragons will eat other individuals of their own species. Groups of them have been observed consuming each other in a chain, each being eaten by the one behind it.
- 3
The air bubble in its stomach is not inhaled — it is swallowed deliberately when the animal reaches the surface, providing the buoyancy needed to float upside-down. If the bubble is lost, the animal sinks.
- 4
Despite being less than 4cm long, a blue dragon has been observed attacking and consuming a Blue Button jellyfish three times its diameter — eating it slowly over the course of an hour.
- 5
The species was described by science in 1777 but remained poorly understood until underwater photography became common — almost nothing was known about its behaviour in the open ocean.