Blue Glaucus

• defensaIt floats upside down at the ocean surface and stores intact stinging cells from the Portuguese men o' war it eats, reusing them, far more concentrated, as a defence of its own.
• It floats foot upwards, so that the silvery blue face we see is in fact its underside.
• It does not swim: it drifts with the wind and the currents, which is why it appears all at once on the beaches after storms.
• It floats on its back by swallowing air: it keeps a bubble in its stomach that holds it at the surface, and it drifts at the mercy of the wind just like the Portuguese man o' war it feeds on.
• It eats Portuguese men o' war and other siphonophores, and it does not digest their nematocysts: it keeps them intact and concentrates them at the tips of its cerata, where it can fire them again.
• And concentrate them it does: the sting of a blue glaucus can be more painful than that of the man o' war itself, because it accumulates the most potent cnidocytes it has been selecting.
• Its colouring is inverted compared with that of almost every other animal, and with good reason: since it floats on its back, the deep blue faces upwards, camouflaging it against the sea when seen from the air, and the silver faces downwards, camouflaging it against the surface when seen from the water.
• It is a hermaphrodite, and all individuals can lay eggs after mating.
• Its mass strandings on beaches are a recurring news story, and it is best not to touch it: it goes on stinging even when dead.

Skeleton type

Invertebrate - no rigid skeleton (mollusc)

Habitat & environment

Surface of the open ocean in temperate and tropical waters

Sources consulted: Thompson y Bennett (1970), Journal of Experimental Biology; Museo Australiano; Valdés y Campillo

Best time: After several days of onshore wind, when it washes up on the beaches