While most nudibranchs live at the bottom of the ocean or in the water column, blue dragons are found on the surface.says Melissa Hobson.
. They float along – held up by an air bubble in their stomach and blown by the winds and currents – until they find something to eat.
Blue dragons are smaller than grapes but that doesn’t put them off attacking much larger venomous animals, including Portuguese men o’war (one of the deadliest animals in the ocean) whose trailing tentacles can stretch below the water for 10 metres or more.
They don’t feel the sting delivered by their prey and even hang onto it so they can use it again later. Keeping these nematocysts (stinging cells) intact, they store them in their finger-like ‘wings’ to use later in self-defence.
These petite predators have various nicknames – blue dragon, blue angel and sea swallow – all inspired by these delicate but deadly ‘wings’.
What are blue dragons?
Arguably one of the most beautiful creatures in the ocean, blue dragons (Glaucus atlanticus) are a type of sea slug that drift along on the ocean’s current hoping to come across their prey.
Being unable to fight the current, these tiny creatures use clever camouflage to blend in with the blue ocean as they float along. And they have a clever trick up their sleeve to stay safe: they eat venomous animals and steal their toxin to use in self-defence in case they are ever under threat.
How big are blue dragons?
Blue dragons are up to 3cm long and weigh between 3 and 100 grams
What do blue dragons look like?
As the name suggests, these nudibranchs look like teeny tiny dragons because of the six ‘wings’ (three on either side) that stretch out from their bodies. Known as cerata, these appendages have several important functions, including breathing and digestion. They are also where they store the stinging cells they steal from their prey – more on that later.
Blue dragons use countershading for camouflage, meaning that their dorsal (back) and ventral (belly) sides are different colours. Their backs are silver but this isn’t what you’d see when looking down from above. That’s because these organisms float upside down at the surface of the water. With their silver-grey backs facing downwards, anything looking up will struggle to make them out against the bright sky.
Meanwhile, they have striking blue bellies that face towards the sky, helping them to blend in with the blue ocean below, should anything be looking down on them. They also have striking dark blue patterns: a bold stripe along their body and a ring in the centre of each of their cerata. The tips of these feathery wings are also dark blue, as if they’ve been dipped in ink.
How do blue dragons hunt?
Growing no more than 3cm long, these tiny critters are often smaller than your pinky fingernail but they don’t let that stop them taking on venomous prey like by-the-wind-sailors (Velella velella), Portuguese men o'war (Physalia physalis), and violet sea snails (Janthina janthina).
Why aren't they affected by their toxic prey?
Blue dragons take a chomp out of their prey using sharp, serrated teeth. Their toxic victims fire stinging cells called nematocysts in self-defence. But the diminutive predators aren’t hurt by the sting – blue glaucus are shielded by a layer of mucus and a protective stomach lining that prevent them from being affected by the venom.
How do blue dragons use the venom?
After taking a nibble, blue dragons don’t digest the nematocysts – they will need those later. Instead, they keep these stinging cells in one piece and store them in their cerata. These are the parts of its body that look like feathered dragon’s wings.
Without a shell, these tiny slugs need another way of protecting themselves from being eaten. So, when under threat, they can deploy the nematocysts to sting their potential attacker. Loggerhead turtles (Caretta caretta) have been found with blue glaucus in their stomachs. Blue dragons have also been known to attack and bite each other.
Are blue dragons dangerous to humans?
Although tiny, these animals can sting – even after they die. Being so small makes them hard to see so they can cause a hazard to people on the beach who might touch or step on one by accident.
If you find one on the beach, don’t pick it up. Remember, they’ve been hanging onto stinging cells from Portuguese men o’war to defend themselves so getting on their bad side is not recommended.
Reportedly, their sting can be even more painful than a man o’war sting because the venom is so concentrated. As well as pain, symptoms are said to include nausea and vomiting. Although it’s very unlikely blue dragons could kill a human, this is possible if someone has an allergic reaction to the venom.
If you do happen to be stung by a blue glaucus, experts advise seeking medical treatment as soon as possible
Where do blue dragons live?
These tiny nudibranchs live in tropical and subtropical waters of the Atlantic, Pacific and Indian oceans. They float (belly-up) right at the surface of the open ocean, using a gas bubble in their stomach to keep them buoyant. They are too weak to swim against the current so they drift along with no control of their direction or destination.
How do blue dragons reproduce?
As simultaneous hermaphrodites, blue angels have both male and female reproductive organs in their bodies at the same time. Despite this, they can’t reproduce alone and need to find another individual to be able to create offspring.
Unable to steer their direction, these hapless voyagers can’t go looking for each other. They just drift along and, with any luck, come across another blue glaucus. After mating, they lay a ribbon of around 16 eggs, which they attach to a floating object in the water, like driftwood. These hatch after just three days.
How long do sea dragons live?
The size of these sea swallows is not the only thing that’s small – they also have relatively short life spans. Estimates suggest that they live for as little as one month or up to one year.
Do they live alone or in groups?
These animals typically live a solitary life. However, because they are at the mercy of the currents, they can find themselves drifting together in large groups. These are sometimes known as ‘blue fleets’ and can wash up onshore after a storm, putting beachgoers at risk if they step on one.
How long do blue dragons live?
A blue dragon's average lifespan is up to one year
What's their scientific name?
Glaucus atlanticus
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