Meet the Glaucus atlanticus, a tiny sea slug that’s only 3 cm long, floating on the surface of an ocean near you. Like many of these uncommon creatures, this one has a lot of names which include a sea swallow, blue angel, blue glaucus, blue dragon, blue sea slug and blue ocean slug. Despite its colorful appearance, this isn’t a creature you’d like to come across as it’s loaded with poison due to its unique diet. It feeds on the venomous Portuguese man o’ war, a creature often mistaken for a jellyfish which also goes by the unsettling name of the “floating terror.”

This small invertebrate eats hydrozoans from the man o’ war, which are fatal to humans, but easily consumed by the Glaucus atlanticus. It has hard disks inside its body that act as protective barriers, secreting a special mucus. After enjoying a meal, the Glaucus atlanticus stores the poison inside its body for the future in order to defend itself. Some scientists think that if this little sea slug has a voracious appetite, it can end up becoming far more dangerous than even the Portuguese man o’ war.

The Glaucus Atlanticus is neither male nor female, but a hermaphrodite with both reproductive organs. After mating, each slug produces eggs, which they lay on driftwood, or on the skeletal remains of their enemies. When food is in short supply, things get a little crazy. When one slug meets another in the neighborhood, rather than wave hello, they’ll simply begin to eat the other head first. Yep, turns out this little pint-sized blue dragon is also a poison-sucking cannibal. Too bad, really, as they are such a lovely shade of blue.

About the Doodlewash

M. Graham watercolors: Cobalt Blue, Cobalt Teal, Ultramarine Blue, and Neutral Tint. Lamy Safari Al Star pen with Platinum Carbon blue ink in a 5″ x 8″ 140 lb. (300 gsm) Pentalic Aqua Journal


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54 thoughts on “The Glaucus Atlanticus

  1. It really is a beautiful creature, but yikes – deadly! Your painting makes it look almost like a lovely glass collectible to be put on display, which is the only way I’d want to meet up with one of these. Very nice, Charlie 👍🏻

  2. Love it’s colors but would hate to meet up with one! Not sure I’d see it at that small size… Another reason to NOT go swimming in the ocean which is fine with me! Hehe! 😜💙🎨

      1. I do like snorkeling too, Charlie! But then I got caught in a riptide on Maui… It was really scary! So unless it is a protected reef, I’m staying on shore! 😬🐠 Where do YOU like to snorkel?! 😄🛳

  3. This is the most beautiful slug I’ve ever seen! That blue has become my favorite blue! Maybe deadly bit so pretty to look at! I’m hoping to do some art this week since it’s my spring break!! Woohoo!! Haha.. ❤️😜❤️

  4. Wow, ice cold. You know, when I first saw this, I thought it so beautiful that it was bound to be something hugely unpleasant, seems I was right… but this is an utterly captivating doodlewash! One to enjoy from a distance, no doubt!

  5. You are educating us, Charlie! I just had to look him up and one of the interesting facts was that “The ventral side of the organism, which actually floats on the sea surface due to the gas float in its stomach, is a brilliantly blue color matching the color of the ocean. The dorsal side, which faces downward into the ocean, is a silvery grey color to blend in with the surface, thus providing protection from predators”.
    Another you could do is the Porpita Porpita, or blue button, which is one of the poisonous jellyfish this slug feeds on. Just a suggestion:-)

    1. That’s awesome!! Thanks so much for including the extra info. These little slugs are endlessly fascinating aren’t they? hehe Love this! Had never heard of a Porpita Portpita… looks like a flower almost instead of a living creature. The Janthina is also on the sea slug’s menu and look pretty cool as well!

    1. Thanks! hehe… it was fun to doodlewash! I list the colors at the bottom in the “About the Doodlewash” section but never sure if anyone sees it! lol I used Cobalt Blue, Cobalt Teal, and Ultramarine Blue (pretty much the only 3 blues I have in my little palette!)

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