The blue dragon – a miniature marvel

Glaucus atlanticus

(Glaucus atlanticus – Blue Dragon, paulhypnos)

I defy any of you to look at this creature and not think it is cool (we’ll skip over the fact that it is actually a sea slug). It looks like a real life pokemon, is generally the size of your thumb yet can deliver a deadly sting. ‘Glaucus atlanticus‘ isn’t a bad geeky name for it either. If you thought the dangerously venomous portuguese man o’ war was a bit scary (which it is), this thing eats them for breakfast. Literally. An impressive feat considering man o’ war’s tentacles can grow up to 50m, whilst an adult blue dragon’s full length sits at around 3cm. These little ocean oddities consume the man ‘o wars in their entirety, harbouring the jellyfish’s venom which is stored in structures known as nematocysts. Much like a nettle packs a punch in the tips of its leaves, this creature concentrates the jellyfish venom in the tips of its feather-like protrusions.

To add to this mounting sense of apprehension you may be feeling for these angels of death , they will occasionally chuck in some casual cannibalism for good measure. Although most predators that try to have a chomp on these creatures would regret their choice of menu, blue dragons also camouflage themselves from above and below in a trick known as countershading. They swallow a little air bubble that is positioned to allow them to float upside down on the ocean’s surface. Whilst their dorsal side (e.g our back) is a greyish colour that blends with the under surface, the striking whites and blues are on its ventral side (e.g our tummy) to blend with how the ocean appears from above. 

Blue dragons are hermaphrodites hence have found a way to sack off the annoyance of finding and putting up with a partner, choosing the favorable ‘I’ll do it myself’ attitude. These beauties can be found in temperate and tropical waters worldwide, so next time you take a holiday to escape the relentlessly burning rays of the English sun, watch out for a creature that is pretty impossible to see but has the potential to kill you. Happy holidays! 


Bieri, R. (1966). Feeding preferences and rates of the snail, Ianthina prolongata, the barnacle, Lepas anserifera, the nudibranchs, Glaucus atlanticus and Fiona pinnata, and the food web in the marine neuston. Publications of the Seto Marine Biological Laboratory14(2), 161-170.

Blake, R. W., & Chan, K. H. (2007). Swimming in the upside down catfish Synodontis nigriventris: it matters which way is up. Journal of Experimental Biology210(17), 2979-2989.

Greenwood, P.G. (2009). Acquisition and Use of Nematocysts by Cnidarian Predators. Toxicon 54(8),  1065-1070.

Piper, R. (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Greenwood Publishing Group, pp. 42–43.

Thompson, T. E.; McFarlane, I. D. (2008). Observations on a collection of Glaucus from the Gulf of Aden with a critical review of published records of Glaucidae (Gastropoda, Opisthobranchia). Proceedings of the Linnean Society of London, 178(2), 107–123.

Thompson, T.E. & Bennett, I. (1970). Observations on Australian Glaucidae (Mollusca: Opisthobranchia). Zoological Journal of the Linnean Society, 49(3), 187 – 197.

Valdes, A. &  Campillo, O. A. (2004). Systematics of pelagic aeolid nudibranchs of the family Glaucidae (Mollusca, Gastropoda). Bulletin of Marine Science75(3), 381-389.


2 Comments on “The blue dragon – a miniature marvel

  1. This is intriguing! So does anything actually successfully eat them? Otherwise, surely, they will just multiply? I was really forward to booking a summer holiday….maybe I’ll take up skiing!

  2. Unfortunately there has been very little scientific research done on them, and their main predators are unknown! However there are several contenders who are immune to the portuguese man o’ war’s venom such as the loggerhead turtle, blanket octopus and ocean sunfish so I would imagine these could get away with a blue dragon sized snack. When food sources are low the blue dragons will also eat each other, resulting in a little self-downsizing!

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