Blue, beautiful and almost angelical, but yet it hides a deadly secret!

This ocean creature has many names such as the sea swallow, blue angel, blue glaucus, blue dragon, blue sea slug and blue ocean slug.

We are talking about Glaucus atlanticus, a small blue sea slug. The slug is part of the shelless gastropod mollusk, belonging to the Galucidae family. The species is pelagic which means they float upside-down using the surface tension in the water to stay afloat.

In many pictures of the slug you can gasp looking at it´s bright blue colours, however in its habitat you would have to keep close eye to even catch a glimpse of it. The slug´s body has a blue side (facing upwards, blending with the ocean) and a slivery side (facing down, blending with the ocean surface). The camouflage makes it hard to spot if you are a predator.

Blue sea slug floating on the surface.

The blue sea slug is pelagic, and there is some evidence that it lives throughout the world’s oceans, in temperate and tropical waters. It has been recorded from the east and south coasts of South Africa, European waters, the east coast of Australia, and Mozambique. Although these sea slugs live on the open ocean, they sometimes accidentally wash up onto the shore, and therefore they may be found on beaches.

Beware of the sting!

Besides the camouflage it has a second weapon which has to do with its favourite meal. The slug eats pelagic creatures, including the feared Portuguese man o´war! When it consumes the venomous siphonophore, it stores some of the stinging nematocysts within its own tissues. Humans handling the slug may receive a very painful and potentially dangerous sting, and may even harm potential predators even more!

Portuguese man o´war stranded on the beach.

Sources: Churchill, Celia K. C.; Valdés, Ángel; Foighil, Diarmaid Ó. (April 2014). “Afro-Eurasia and the Americas present barriers to gene flow for the cosmopolitan neustonic nudibranch Glaucus atlanticus”, Valdés, Ángel; Orso Angulo Campillo (November 2004). “Systematics of Pelagic Aeolid Nudibranchs Of The Family Glaucidae (Mollusca, Gastropoda)”, MILLER, M. C. (January 1974). “Aeolid nudibranchs (Gastropoda: Opisthobranchia) of the family Glaucidae from New Zealand waters”. Zoological Journal of the Linnean Society